Union Internationale des cie11ccs Bwlogiques
ORGANISATION INTERNATIONALE DE LUITE BIOLOGIQUE ET INTEGREE CONTRE LES ANIMAUX ET LES PLANTES NUISIBLES
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t».:st '�' ISBN 92 9067 03& X �,:-··11 WORKING GROUP i�1Jj • INTEGRATED CONTROL IN CEREAL 1 CROPS :, /'
GROUPE DE TRAVAL ., •LUTTE INTEGREE EN CEREALES
PROCEEDINGS OF THE MEETING AT QOTTINQEN ( F . R • Q . ) 21 22 MARCH 1990
EDITED BY C. A. DEDRYVER EDITE PAR
IOBC / WPRS BlA.LETIN 1991 /XIV/ 4 BULLETIN OILB / SROP
InknUdional Union of Biological Scienus
INTERNATIONAL ORGANIZATION FOR BIOLOGICAL AND INTEGRATED CONTROL OF NOXIOUS ANIMALS AND PLANTS
WEST PALAJIWitCTIC UOIONAL SECTION
1
IOBC OILB WPRS SROP
WORKING GROUP • INTEGRATED CONTROL IN CEREAL CROPS •
PROCEEDINQS OF THE MEETING AT GOTTINGEN ( F . R. G.) FROM 21 - 22 MARCH 1990
GROUPE DE TRAVAIL • LUTTE INTEGREE EN CEREALES
COMPTE - RENDU DE LA REUNION A GOTTINGEN ( R . F. A. ) DE 21 - 22 MARS 1990
EDITED BV C. A. DEDRYVER EDITE PAR
IOBC / WPRS BULLETIN f!J!Jf /XIV/ 4 BULLETIN OILB / SROP
Union Internationale des Sciences B1otogiques ORGANISATION INTERNATIONALE DE LUTTE BIOLOGIQUE. ET INTEGREE CONTRE LES ANIMAUX ET LES PLANTES NUISIBLES SECTION REGIONALE QUEST PALEARCTIQUE International Union of B1ological Sciences INTERNATIONAL ORGANIZATION FOR BIOLOGICAL AND INTEGRATED CONTROL OF NOXIOUS ANIMALS AND PLANTS WEST PALAEARCTIC REGIONAL SECTION
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Pour la promotion des systemes de pro.tection int6gr�e For the promotion of integrated protection systems i
AVANTPROPOS
La reunion bisannuelle de notre groupe de travail a ete organisee par notre collegue Michael Poehling et s'est tenue les 21 et 22 mars 1990 a l'Institut de pathologie vegetale et de protection des plantes de l'Universite de Göttingen (RFA). Elle nous a donne l'occasion de celebrer avant la lettre la reunification de l'Allemagne, puisque 5 collegues de la section de protection des plantes de l'Universite de Martin Luther de Halle (a l'epoque en RDA) ont activement participe a cette reunion et ont demande a faire partie du groupe.
La reunion a donne lieu a 17 communications portant sur la biologie et la dynamique des populations de pucerons des cereales et les methodes de prevision des pullulations, l'epidemiologie de la jaunisse nanisante de l'orge et la prevision des epidemies, l'action des hymenopteres parasitoides et hyperparasitoides et le röle des predateurs polyphages, particulierement en relation avec les traitements insecticides. Enfin une communication traite du puceron Diuraphis noxia, nouveau ravageur introduit en Amerique du Nord, et de l'inventaire de ses ennemis naturels dans ses zones d'habitat traditionnelles et une autre resume les recherches entreprises en France sur la Pyrale du mai"s.
Au cours de la discussion qui a suivi, trois sujets de collaboration ont ete proposes pour les prochaines annees
Le premier projet. propose par Th. Basedow consiste a renforcer les liens entre les quelques collegues specialises dans l'etude des predateurs polyphages autour d'une experimentation multisite utilisant des methodes standard.
Le second projet a ete propose par M. Poehling et C.A. Dedryver, autour de l'epidemiologie de la jaunisse nanisante de l'orge ; il consiste a comparer la biologie des vecteurs (particulierement les modes d'hivernation) et les differentes souches de virus presentes, selon un arc de cercle allant du Nord de l'Espagne (Lerida) au Nord de l'Allemagne (Göttingen) en passant par la France (Rennes) et l'Ouest de l'Allemagne (Stuttgart). Les conclusions de ce projet seront debattues au cours de la prochaine reunion ou des virologues seront invites.
Le troisieme projet a ete propose par C.A. Dedryver, il consiste a creer une banque de donnees sur les fluctuations de populations de pucerons des cereales, au depart dans trois pays, France, Allemagne et Grande Bretagne. Elle serait constituee de resultats ii de comptages et d'observations et serait a la disposition de tous avec l'accord des parties interessees. Cette banque de donnees,qui dans certains cas rassemblerait plus de 10 annees d'observations, permettrait des comparaisons inter-regionales du plus grand interet.
L'ensemble des participants a, pour terminer, adresse ses remerciements chaleureux a M. Poehling pour l'excellente organisation materielle et scientifique de la reunion.
L'animateur C.A. DEDRYVER iii
FOREWORD
The bisannual meeting of the working group was organised by our colleague st Michael Poehling and was held on 21 and 22nd March 1990 at Göttingen (FRG), Institut of Plant pathology and Plant protection of the University. This meeting gave us the opportunity to celebrate in advance the reunification of Germany, because five colleagues of the plant protection service of the University Martin Luther of Halle (previously in GOR) attended it and asked to belang to our group. Twenty six participants belonging to 7 countries attended the meeting, and 17 papers were presented. The main topics were . biology, population dynamics of cereal aphids and forecasting methods . epidemiology of BYDV and epidemics forecast
. role of hymenopterous parasitoids an d hyperparasitoids . role of epigeal predators, specially in relatioP.with insecticides sprays.
Another communication concemed Diuraphis noxia, a newly introduced pest in America and the inventory of its natural enemies in the old world and finally, a last paper summarised the researches in France on the european com barer.
From the discussion, 3 new projects were planned for the following years .
. The first project was proposed by Th. Basedow and consisted to strenghten links between colleagues working on epigeal predators with a common experiment using standard methods . . The second project was proposed by M. Poehling and C.A. Dedryver on BYDV epidemiology. Its aim was a comparison of vectors biology (specially overwintering) and virus strains on different locations : North of Spain (Lerida), France (Rennes), Western and Northern Gerrnany (Stuttgart and Göttingen). Virologists will be invited at the next meeting. . Tue third project was proposed by C.A. Dedryver and consisted to create a data bank on cereal aphids (First in France, Germany and U.K.), using the counting data collected in the 3 countries. This data bank will concern in some cases more than 10 years of observations and will a!low interesting interregional comparisons. iv
The advances in these projects will be discussed at the next meeting. Finally the whole participants thanked M. Poehling and his staff for the excellent material and scientific organisation of the meeting.
The convenor C.A. DEDRYVER V
LISTE DES PARTICIPANTS/LIST OFTHE PARTICIPANTS
Thies BASEDOW Institut für Phytopathologie und angewandte Zoologie, Universität Gießen, Ludwigstr. 23, 6300 Gie�en, BRD. Christian BORGEMEISTER Institut für Pflanzenpathologie und Pflanzenschutz, Universität Göttingen, Grisebachstr. 6, 3400 Göttingen,BRD. PetraCHRISTIANSEN-WENIGER Institut für Phytopathologie, Universität Kiel, Olshausenstr. 40-60, 2300Kiel, BRD. Jordi COMAS Institut de Recera i Technologia Agroalimentaries, Universitat Politecnica de Catalunya, CentreR+D de Lleida,Alcade Rovira Roure. 177, 25006 Lleida,ESPANA Roger DE CLERCQ Rijksstation voor Nematologie en Entomologie, Universiteit Gent, Burg. Van Gansberghelaan 96, B-9220 Merelbeke, BELGIE- BELGIQUE. CharlesDEDRYVER INRA Le Rheu,Laboratoire de Recherches de la Chaire de Zoologie, Domaine de la Motte au Vicomte, B.P. 29, 35650 Le Rheu. France. Axel DINTER Institut für Pflanzenpathologie und Pflanzenschutz, Universität Göttingen, Grisebachstr.6, 3400 Göttingen BRD. UlfGRÖGER Institut für Phytomedizin, Universität Hohenheim, Otto-Sander-Str. 5, 7000 Stuttgart 70,BRD. Francis GRUBER European Parasite Laboratory, rue de la Masse 13-17, 78910 Orgerus-Behoust, France. Helmut HAARDT Institut für Pathologie, Universität Kiel, Olshausenstr. 40-60, 2300Kiel, BRD.
Udo HEIMBACH BBA, Messeweg 11/12, 3300 Braunschweig, BRD. Juha HELENIUS Department of Agricultural and Forest Zoology, University of Helsinki, SF00710 Helsinki, Finland. Falco HOLZ Sektion Pflanzenproduktion, Martin-Luther U niversität Halle-Wittenberg, Ludwig Wucherer-Str. 2. Postamt 1, 0-4010 HALLE (Saale),BRD. Martin KREUTER Sektion Pflanzenproduktion, Martin-Luther Universität Halle-Wittenberg, Ludwig Wucherer-Str. 2. Postamt 1, 0-4010 HALLE (Saale)�BRD. vi
Guy LATTEUR Station de Zoologie Appliquee, Chemin de Liroux 8, B-5800 Gembloux, BELGIQUE BELGIE GerhardLAUENSTEIN Landwirtschaftskammer Weser-Ems, Pflanzenschutzamt, Postfach 2549, 2900 Oldenburg, BRD. Frany<>iseLECLERCQ-LE QUILLEC INRALe Rheu, Laboratoire de Recherches de la Chaire de Zoologie, Domaine de la Motte au Vicomte, B.P. 29, 35650 Le Rheu. France. Marita LÜBKE Sektion Pflanzenproduktion, Martin-Luther Universität Halle-Wittenberg, Ludwig Wucherer-Str. 2. Postamt 1, 0-4010 HALLE (Saale), BRD. Hans-Michael POEHLING Institut für Pflanzenpathologie und Pflanzenschutz, Universität Göttingen, Grisebachstr. 6, 3400Göttingen, BRD. XavierPONS Institut de Recerca i Technologia, Agroalimentaries, Universitat Politecnica de Catalunya, Centre R+D de Lleida, Alcade Rovira Roure. 177, 25006Lleida, ESPANA. Jean-Christophe SIMON INRA Le Rheu, Laboratoire de Recherches de la Chaire de Zoologie, Domaine de la Motte au Vicrnnte, B.P. 29, 35659 LeRheu,·France. NutchareeSIRl Institut für Phytopathologie, Universität Kiel, Olshausenstr.40-60, 2300 Kiel, BRD. Keith SUNDERLAND Institute of Horticultural Research, Worthington Road Littlehampton, West Sussex BN17 6LP, UK. Brigitte TENHUMBERBG Institut für Pflanzenpathologie und Pflanzenschutz, Universität Göttingen, Grisebachstr. 6, 3400Göttingen, BRD. Bemd ULBER Institut für Pflanzenpathologie und Pflanzenschutz, Universität Göttingen, Grisebachstr. 6, 3400Göttingen, BRD. ChristaVOLKMAR Sektion Pflanzenproduktion, Martin-Luther Universität Halle-Wittenberg, Ludwig Wucherer-Str. 2. Postamt 1, 0-4010 HALLE (Saale), BRD. Theo WETZEL Sektion Pflanzenproduktion, Manin-Luther U niversität Halle-Wittenberg, Ludwig Wucherer-Str. 2. Postamt 1, 0-4010 HALLE (Saale), BRD. vii
SOMMAIRE/CONTENTS
Page A vant-Propos ...... i Foreword ...... iii Liste des participants ...... v
POEHLING H.M., TENHU MBERG B., GROEGER U. : Different pattern of cereal aphid population dynarnics in northem Hannover-Göttingen) and southem areasof West Gerrnany...... 1 LATI'EUR G., OGER R. : Winter wheat aphids in Belgium : prognosis and dynarnicsof their populations ...... 13 HOLZ F. : A model-based catalogue of case studies as a tool for decision making in the controlof the cereal aphid Macrosiphum (Sitobion) avenae in winter wheat...... 35 VOLK MAR C., WETZEL Th. : On the occurence and controlof insect pests affectingwinter wheat earsin practice ...... 42 SI MON J.C., DEDRYVER C.A. : Variabilite interclonale dans la production de forrnessexuees chez le puceron des cereales Rhopa/osiphumpadi ...... 51 BORGEMEISTER C.,· POEHLINGH:M: : Reasons for and consequences of the serious B.Y.D.V.infestation in Northem Gerrnany.1989 ...... 60 LECLERCQ-LE QUILLEC F., DEDRY VER C.A.: Dynamique des vecteurs et des virus de la jaunisse nanisante de l'orge dans le bassin de Rennes a l'automne1989 ...... 67 CO MAS J., PONSX., ALB A JES R.: Advances in the knowledge ofB.Y.D.V. epidemiology in Spain...... 75 DEDRYVER C.A., CRE ACH V., RAB ASSE J.M., NENON J.P. : Spring activity assessment of parasitoids in Western France by experimental exposure ofcereal aphids on trap plants in a wheat field...... 8 2 CHRISTIANSEN-WENIGER P.: Some aspects ofhost selection by two aphid hyperparasitoids : Asaphes vulgaris Wl.k.and Asaphes suspensus (Nees) (Hymenoptera : Pteromalidae) ...... 94 GRUBER F., PO PR AWSKI T.J., REY E. : Survey for natural enemies of Diuraphis noxia (Mordvilko) in Eurasia ...... 10 2 DE CLERCQ R., CASTEELS H., JANSSENS J. : Influence of pesticides on the epigeal arthropod faunain laboratory tests...... 110 BASEDOW Th., AL NAJJ AR A.: Nitrogen , plant growth regulators , pests and diseases , and the economy of growing winter wheat in Northern Gerrnany. . _ ...... 115 viii
HELENIUS J. : Integrated control of Rhopalosiphum padi, and the role of epigeal predators in Finland...... 123 HEIMBACH U. : Effects of some insecticides on aphids and beneficial arthropodsin winter wheat...... 131 LÜBKE M.: Activity and population density of epigeal arthropods in fields of winter wheat...... 140 HAWLITZKY N. : Travaux realises en France, a !'Institut National de la Recherche Agronomique, sur la Pyrale du Mai"s, Ostrinia nubilalisHbn. (Lep.Pyralidae )...... 145 DIFFERENT PATTERN OF CEREAL APHID POPULATION DYNAMICS IN NORTHERN (EANNOVER-GÖTTINGEN) AND SOUTHERN AREAS OF WEST GERMANY H.M. Poehling1, B. Tenhumbergt und u. Groeger2 1Institute of Plant Pathology, University of Göttingen, Göttingen, FRG 2Institute of Phytomedicine, University of Hohenheim, Suttgart-Hohenheim, FRG Summarv Studies in different regions of Western Germany (Hannover, Göttingen, Stuttgart-Hohenheim) showed that the variability in cereal aphid population pattern decreased when a regional differentiation was performed. Therefore a more regional forecast of cereal aphids is necessary to improve the current West German threshold model. A multiple regression analysis according to Entwistle and Dixon (1986) seems to be a promising approach to predict peak densities with a higher accuracy. One reason for the different development of cereal aphids in Hannover and Stuttgart seems to be the variable coincidence between aphids and syrphids. Possible reasons for that are discussed. 1.1 Introduction Today the control of cereal aphids in winter wheat in Western Germany is based on estimates of aphid density during ear emergence (EC 55/59) and the end of flowering (EC 69). If the critical value of 1 aphid /ear or flag leaf is exceeded, the farmers are recommended to spray (Basedow et al., 1989). This means that the evaluation of aphid populations is often based on a single estimate of numbers of aphid per ear and flag leaf (or the percentage of infested tillers). The current threshold is derived from a series of investigations during 1980 - 1983, in which effects of aphid elimination by spraying with pirimicarb at different growth stages and different aphid densities on yield were investigated. Underlying is the assumption that if this critical aphid density is reached or exceeded - even at the end of anthesis - the pest will still increase with a maximum rate reaching peak densities above an injury level between EC 71 and 75. By using this very simple model unnec. . ...essary applications of insecticides could be avoided on an average of nearly 50 % compared wi th prophylactic treatments. On the other hand still large areas are still treated although in many cases aphids never reach damaging densities. - 2 -
Area Hannover /Hameln (North)
Aphlda/ear•flaglaaf 50-;....:-----=------,
40·
30
20
10
o�����====:=�===----,----.,---..::::'.1' EC 55 EC 81 EC 66 EC 89 EC 71 EC 75
HMe• --+- HM 815 1 � HM 86 2 -e- HM 88 1-"""*- H 17 �H88 �H89
Fig .1 Population pattern of cereal aphid·s fro111 selected fields in Hannover/Hameln bettween 1984 and 1989. Göttingen 83-89 (North)
aphlda/ea....-flagleaf 40..-'-----=------,
30
20
10
EC 56 EC 61 EC 66 EC 69 EC 71 EC 76
- Oö8S --+-oö84H _.- Gö84K1 --EI-Qö86H -41- Gö 84 K2 -+- Gö 86 H � Gö 89
H:Hanaltn (1988); K, Kuo •t cl. (1989)
Fig. 2 Population pattern of cereal aphids in Göttingen between 1983 and 1989.
In Göttingen beside all variations two more general types of population patterns could be observed: 1. Relative high densities at booting or early anthesis were followed by a low increase. Peak densities were reached at EC 69 or even before. - 3 -
In order to improve the accuracy of this model we made an attempt to evaluate the variability of cereal aphid population pattern between different years and different regions in Germany. In addi tion we checked the multiple regression system of Entwistle and Dixon (1986) for its usefulness to improve the forecasting of aphid peak densities. Differences in regional pattern are discussed by especially considering the role of syrphid larvae as one key factor of the cereal aphid population dynamics. 1.2 Results and discussion Fields Data were evaluated from different regions: - Stuttgart-Hohenheim: This area does not belong to the outbreak areas in Germany and is characterized by a rather high heterogenity of the landscape with small fields predominating (Schier, 1988; Ohnesorge and Schier, 1989). - Hannover/Hameln: In this typical outbreak region intensive wheat production is performed on larger fields, there are often only small areas covered with pastures or hedges surrounding the fields. - Göttingen: The Göttingen area is quite similar to Hannover (100 km to the south), but particularly the small experimental fields in which the trials were conducted showed more of the features described above for Stuttgart-Hohenheim. Cereal aphid pattern The typical pattern of cereal aphid population dynamics in the regions of Hannover and Göttingen are shown in Fig. 1 and Fig. 2. In Hannover the population curves show a high degree of similarity and consistency in relation to wheat growth stages (Poehling, 1988). Except for 1989 in all cases the peak densities were reached between EC 69 and EC 75. Averaging the density values at different growth stages resulted in a "mean" pattern shown in Fig.4. In most years Sitobion avenae was the predominant species although Metopolophium dirhodum always immigrated earlier except from those years with anholocylic hiberna tion of S. avenae. Large differences however occurred bet ween different years if peak densities were concerned. The pattern of 1985, 1988 and 1989 fitted very well to the threshold model of Basedow et al., (1989) but in 1984, 86 and 87 aphid peak densities were far below 10 aphids/ear and flag leaf. According to the threshold model in the latter case insecticides bad to be sprayed too. - 4 -
2. Low densities at the beginning of flowering were followed by a late, rapid and intensive population growth at the end of anthesis (Kuo et al., 1989). In consequence the "mean" growth curve for this region (Fig. 4) is very different with the one of the Hannover area.
Hohenheim � Münchingen (South)
. aphld•'_::_••:::.•_•l_::_l•;__le •f______20 ;::::::.::_:::. :.: 1
15
10
5 ------
EC 65 EC 81 EC 86 EC 89 EC 71 EC 75
- Hol3S -+- Ho 86S -e- Ho BIS -*- HoN _._ MU 89
S: Schlar (1918)
Fig. 3 Population patttern of cereal aphids from selected fields in Hohenheim from 1984 - 1989. "Mean· abundance of cereal aphids (Hannowr.Göttlngen.Hohenh&im)
aphlda/Hr+IIIIOlu! 20..;.::.----'-----"------,
1�"-,, 15 1 / ", / /' 10 �j / 5 -�'l------/ 0 +-----r----�--r-----.----- .------i EC 55 EC 81 EC 85 EC 69 EC 71 EC 75
- Hanonr "'f\Otth 1 -i- Gattln;en nor1h 2 ....,._ HGhenhelm aouth
Fig. 4 "Mean" population pattern of cereal aphids from three dif.ferent regions in Western Germany - 5 -
The development of ceral aphid populations in Hohen heim exhibited larger differences in relation to the pattern of the two other localities (Fig. 3). In most cases real gradations could never be obser ved although aphid densities were rather high at booting and early anthesis. The decline of aphid populations often started rather early, sometimes already at mid anthesis (Schier, 1988). In all years M.:.. dirhodum was the domina ting species. s. avenae appeared late and reached only small densities although the physiological conditions of the host-plant were convenient for this species too.
Multiple regression analysis An interesting approach·.to the calculation of the peak density of Sitobion avenae with relative simple means using a multiple regression analysis was described by Entwistle and Dixon (1986). A similar calculation was per formed for the here described population pattern, by using whole aphid numbers (S. avenae + M.:.. dirhodum) on ears and flag leafs. Peak densities were correlated with either the aphid densities at different times (EC 55-69) or the rate of increase between growth stages or both (multiple regres sion). For the Hannover area a close relation existed bet ween aphid densities at distinct times during flowering and peak densities (Table 1, Fig.5). Corresponding to the re sults_of Bntwistle and Dixon (1986) the significance rose with progressing growth stages. The rate of increase showed a much smaller correlation (Table 1, Fig 5). An explana tion for this phenomenon could be that the parameter "density" explained most of the variation of peak density in this region and t.hat only minor effects of other regula tion factors - like natural enemies - influenced aphid de velopment during this period. Further more the rate of in crease may be strongly influenced by extended periods of immigration which was not considered in these studies. A multiple correlation using both parameters improved the accuracy of the prediction, which may be indicated here by the high r-squared values (Table 1) and the 1:1 line of predicted versus observed peak densities (Fig. 5). Conside ring the differences between observed and predicted values the accuracy of the modal seems to be unsatisfactory. On the other band the model provided a sufficient accuracy to select cases with critical densities. That means an excee ding of relevant infestation levels between 5 and 10 aphids per plant (Table 2). - 6 -
Table 1 Regression analysis (Hannover - north} A: Relation of mean peak number of aphids * (y) to the mean nwaber of aphids (x} at different growth stages (BC). (Hannover - north} BC 55 ln y = 2.833 + 0.471 ln X r = 0.53 r Z = 28.15 % BC 61 ln y = 2.000 + 0.799 ln X r = 0.83 rZ = 66.16 % BC 65 ln y = 1.087 + 0.415 ln X r = 0.82 r2 = 68.13 % BC 69 ln y 0.246 + 1.152 ln X r = 0.89 rz = 80.29 % 8: Relation of mean peak number of aphids * (y) to the rate of increase in mean number of aphids/ day (x) r EC 55-61 ln y = 2.519 + 0.416 ln X r=0.043 r Z= 0.19 % r BC 61-65 ln y = 1.758 + 3.614 ln X r=0.350 r2=,12.11 % r Be 65-69 ln y = 1.756 + 5.645 ln X r=0.411 rll=l6.94 % r BC 55-65 ln y = 1.697 v 3.830 ln X r=0.307 rz= 9.45 % r EC 61-69 ln y = 1. 723 + 4.507 ln X r=0.367 r2=13.50 %
C: Multiple regression of the mean peak number of aphids (y} and the mean number of aphids (x1.) and the rate of incr.ease. {X2) BC 69 / r BC 65-69 ln y = -0.277 + 1.103 ln X1 + 4.117 X2 r Z "" 86.04 % EC 69 / r BC 61-69 ln y = -0.328 + 1.139 ln X1 + 3.301 X2 ra = 83.84 % BC 65 / r EC 61-65 ln y = 0.531 + 0.962 ln X1 + 2.236 X2 rZ = 65.06 % BC 65 / r BC 55-65 ln y = 0.138 + 0.967 ln X1 + 3.837 X2 r* ..70.85 % EC 61 / r EC 55-61 ln y = 1. 514 + 0.829 ln Xt + 1.952 X2 rz = 61.50 %
Also for the Göttingen area relatively precise pre dictions were obtained by the multiple regression analysis, but concerning the too low number of evaluated fields (i.e. 7) the resul ts have to be regarded as prelimenary until now. It has still to be mentioned that a multiple regres sion for both areas {Hannover + Göttingen } - although in this case 20 sites were used for the calculation - de creased the accuracy of the predictions ( r-squared values in Table 3). - 7 -
This is an additional indication for the regional specification of the population dynamics of cereal aphids and stresses the need for more differentiated regional forecasting systems. In general i t could be summarized that the variabi lity in cereal aphid population pattern decreased when a regional differentiation was performed. Not only between southern and northern areas very different types regularly occur but also in areas relative close to each other signs of more or less regularly recurrend pattern can be noticed. Therefore more regional forecast of cereal aphids is neces sary to improve the current West German threshold model. The multiple regression analysis seems to be a promising approach to an achievement of a higher accuracy for the prediction of peak densities but this assertation has to be confirmed in future by using more data to calculate the re presentative rsgression equations. Last but not least a va lidation with independend data has to be performed.
Table 2 Comparison of observed and predicted values for peak density of &phids per ear and flag leaf. Multiple regression - EC 69 /r EC 61 - 69) (Hannover - North 1) Field observed predicted relative difference (observed ... 100 %) 1 (1984) 6.8 5.9 12.70 % 2 (1985) 44.7 42.4 5.06 % 3 (1985) 36.3 52.9 45.96 % 4 (1985) 14.0 12.9 7.60 % 5 (1985) 36.3 36.4 0.02 % 6 (1986) 6.5 5.2 20.00 % 7 (1986) 2.7 4.2 54.76 % 8 (1987) 5.7 6.7 17.50 !II 9 (1988) 37.5 17.8 53.39 % 10 (1989) 11.4 14.8 29.74 % - 8 -
Table 3 Comparison of ra- values from multiple regression analysis (Ha = Hannover; Gö = Göttingen Ha Gö Ha + Gö X1 Xz
69 65 69 86.48 41.52 71.47 69 61 - 69 83.44. 96.42 76.55 65 61 - 65 65.06 62.80 53.74 65 55 - 65 70.85 47.95 57.73 61 55 - 61 61.50 57.57 59.86 X1 = Aphids / ear + flaf leaf Xz = rate of increase
peak density <---> density EC 69 peak density <---> rate of increase Hannovtf' - north HIIMO'rtt" - nortJ'\ T·r 1.
!.!I 2.:! 2.6 o., 0.2 0.3 o., J ... 1ph1d density EC SB rat& of 1ncreese EC S1 - 691
Multiple regression EC 69 / r EC 61-69 Q,l..annover- Nortl'I 1)
' 2 �retHcteQ' aprüd puk d�ns1ty
Fig. 5 Regression analysis - Single linear regression (A and B) and multiple linear regression 1:1 line {C) - 9 -
Effects of syrphid larvae Irrespective of the possibility to use the regression analysis it is important to analyse the reasons for the very different population pattern of cereal aphids in the northern and southern areas. We believe that especially in the southern areas {SchieT, 1988) and to a certain extent also in the northern parts {Poehling and Borgemeister 1989) aphid specific predators particularly syrphids as well as in some years also coccinellids, have proved to be one key factor which regulates the population dynamics of the cereal aphids. In 1988 and 1989 we simultaneously analysed the po pulation dynamics of syrphids in cereal stands in Hannover and Stuttgart. 1988 in both regions first cereal aphids could be observed nearly at the same time, but only in Han nover a typical gradation followed. In Hohenheim syrphids {mainly Episyrphus balteatus) immigrated about two weeks earlier than in the northern area (Fig. 6). The important (voracious) larval population was established before the aphids reached their highest multiplication rates. However in Hannover syr9hid larvae appeared too late to prevent a first strong increase of aphid densi ty. They were mainly responsible only for the accelerated aphid decline. In 1989 very similar tendencies could be observed (Fig. 6). In this year the pest already reached the high infestation level of more than 2 aphids per plant before booting. Such a density is regularly sufficient to stimu late egg laying of syrphids, but again the syrphids only colonized the fields in the southern area in time. The ob served regional differences are probably due to a bad syn chronisation in time with different migration pattern bet ween specialists and aphids. These statements do not mean that syrphids are belie ved to be the only important regulation factor in the southern areas but the relation between aphid increase and the appearence of syrphids is rather impressive. The reasons for this observations are still hypothetical today: Ohnesorge (Ohnesorge and Schier, 1989) formulated two possible causes: 1. In the southern parts syrphid development is favoured, as in many other areas in southwestern Germany, too, by the high heterogenity of the landscapes. Aphid predators can easily find suitable habitats close to the fields all year round and especially in spring. 2. The early occurence of M. dirhodum might induce aphid predators to immigrate into"the cereals rather early, too. - 10 -
Population development of syrphid larvae and ceree.l aphid11
Slultaart (IIOUlh) 1988
"il-!. to ·- - apbldo D,2il 811 � au D,20 a + 21 a.1& .. g ID ..... & ,1 D,10 ,l; lD 1 & D,D& � D D,IJD 11 17 23 21i 6 11 17 23 211 4 lune July Aug
HuulDYer (norlh) 11188 D,l!li "il to II.III j: 1:e II D,11 tu III ..... D,111 u -....1& ID .:1 11,1111 :a 5 i � D 11 23 zo 6 11 17 23 211 4 lune lul:, Aug
Population developmenl of IIJ!Phid larvae tmd cereel aphid11
Stuttgart (south) 111811 D.10 "iJ lR ·- -aplddl 'Q1a o.118 a � l •. ll,DII...... ; 0,!11 = ...... • 0.DI .5 a.oo 1: 30 11 17 23 211 11 17 6 lune 6 lul:, Ma:,
Hanno'l'llr (norlh) 111811 D,10 "il IR j1a D,118 � 0,118 i l .• ...... 0,!11 .. • . E � 1 a.aa .!! t D 30 i1 17 23 211 6 11 17 6 June Jul:, Ma:,
Fig 6 Cereal aphids a11d syrphid larvae in winter wheat in different regions in Western Germany (1988 and 1989). - 11 -
These are rather interesting and to a certain degree also convincing arguments, but they do not solely explain all the observations. Especially in 1989 aphid densities in northern areas were higher than in Hohenheim early in the season, probably due to a large amount of succesfully hi bernating anholocyclic clones of s. avenae. Climatic condi tions for the hibernation of syrphids were also excellent and large colonies of aphids and pollen on early blooming shrubs were available for a possible spring generation, but the syrphids in Hannover still immigrated into the cereals as late as in former years. It is well known that syrphids can undertake large migrations in autumn and spring. It has to be evaluated whether a long distance migration from southern areas can be responsible for the above described time-lag. Unfortuna tely we really know nothing today about the hibernation and spring development of the important eurytopic syrphid spe cies in the northern areas of Germany. Acknowledgement This work was supported by the German Research Foundation (DFG).
References Basedow, T., Bauers, C. and Lauenstein, G, (1989). Ergeb nisse vierjähriger Untersuchungen zur gezielten Be kämpfung der Getreideblattläuse (Hom., Aphididae) im intensiven Winterweizenanbau: optimaler Termin und Bekämpfungsschwellen. Mitt. Biol. Bundesanstalt, 254. Entwistle, J.C. and Dixon, A.F.G. (1986). Short-term fore casting of peak �opulation density of the grain aphid (Sitobion avenae) on wheat. Ann. appl. Biol., 109, 215-222. Hansen, W. (1986). Die Populationsdynamik von Blattläusen an Weizen in Abhängigkeit von der Qualität des Phloemsaftes bei unterschiedlicher N-Düngung. Diss. Universität Göttingen. Kuo-Sell H.L., Holthusen, C., Quentin, M., Wieduwilt, A. und Wilhelms, A. (1989). Wechselwirkungen zwischen Getreideblattläusen (Homoptera: Aphididae) und Para sitoiden (Hymenoptera: Aphididae) und ihre Bedeutung für die Blattlausbekämpfung in Winterweizen. Med. Fac. Landbouww. Rijksuniv. Gent, 54/3a, 883-893. Ohnesorge, B. and Schier, A. (1989). Regional differences in population dynamics of cereal aphids and their bearing on shortterm forecasting. Med. Fac. Land bouww. Rijksuniv. Gent, 54/3a, 747-752. - 12 -
Poehling, H.M. (1988). Influence of cereal aphid control on aphid specific predators in winter wheat. Bntomol. gen., 13, 163-174. Poehling, H.M. and Borgemeister, B. (1989). Abundance of coccinellids and syrphids in relation to cereal aphid density in winter wheat fields in northern Germany. WP�S Bulletin, XII/1, 99-107. Schier, A. (1988). Untersuchungen zur Populationsdynamik der Getreideblattläuse unter besonderer Berück sichtigung ihrer natürlichen Gegenspieler. Diss. Univ. Hohenheim - 13 -
Winter wheat aphids in Belgium : prognosis and dynamics of their populations.
LATTEUR, G. (*) and OGER, R. (**)
(*) Station de Zoologie appliquee, Chemin de Liroux, 8, 5030 Gembloux, Belgique.
(**) Bureau d'Informatique et de Statistique appliquees, Avenue de la Faculte d'Agronomie, 22, 5030 Gembloux, Belgique.
SUMMARY
From 1972 to 1989, the evolution of the aphid populations and of their main natural enemies was observed in 90 winter wheat fields in the Belgian cereal area. The observations were made once a week throughout the period of aphid develcpment.
A rational control method against these aphids has been developed. It is based on the knowledge of the influence of the aphids (M. dirhodum + S. avenae ) on the yield according to the importance of their populations and on a simple linear multiple regression model using for the forecast the density of aphids per tiller and that of their main specific enemies (parasitoids, entomophthorales and larvae of syrphids) .at the growth stage "kernel formation".
Finally, the average evolution of populations of cereal aphids and of their specific enemies is commented and compared with the forecast of the general model.
1. Introduction
Metopolophium dirhodum (Walker) and Sitobion avenae (F.) appear to be the main summer entomological pests in wheats in Western Europe. However, because of the action of numerous abiotical and chiefly biotical factors, the developmen t of their populations is very variable from year to year and therefore their impact on the cereal yield varies from nought kilo to several hundreds of kilos by hectare. As the years with weak and harmless aphid populations are defini tely more numerous than the years wi th important and harmful ones, it is useful for the profitability of the crop and the protection of - 14 -
environment to try to control these depredators cnly when this is economically justified.
There are three main methods to help the farmers to manage the protection of their crops against these pests only when need be.
The first one consists in advising the farmer only to act if the aphid density reaches a given treshold, for example one ear out of two colonized by at least one aphid. But he has to do the observations himself and he is the only judge of the seriousness of the situation. It is the method which prevails in France nowadays (Fougeroux 1990).
The second one consists in giving the farmer a scientific and computerized supervision. He is then given advice on condition that he provides a minimum of information, chiefly an observation of the presence or the absence of aphids on a small number of tillers. The first system proposed to farmers is "Epipre" issued from Holland (Rijsdijk & al. 1981). In England the "Prestel Farmlink" system similar to Epipre has been working since 1985 (Wratten & al. 1987).
The third method consists in asking the farmer for no observation at all and in advising him by referring to precise observations made by a team of specialists in reference fields lying in the region to protec.t. Since. 1986 this method has been used in Belgium for 3 reasons
1) very few Belgian farmers are willing to do the required observations by themselves;
2) the area to protect being small, the situation hardly varies from field to field during the same year and a good prognosis can usually be made for all the fields ;
3) it is better to include the main specific aphid enemies in the prognosis in order to reduce the risk of error, which implies that the observations must be done by specialists.
2. Descr�ption of the Belqian advisinq method.
2. 1. The method
The prognosis is based on the knowledge of the influence of the aphids (M. dirhodum + S. avenae ) on the yield according to the importance of their populations and on a simple multiple regression model which makes it possible to predict the maximum which should be reached by the populations.
The relationship between the increase in yield obtained after an aphicide treatment and the aphid populations at peak was - 15 -
determined with the results of 40 trials in fields. Thanks to that relationship, i t is possible to determine the economic treshold corresponding to the total cost of an aphicide treatment in wheat. So, if in the present economic conditions, one assesses that the cost corresponds to about 170 kg of wheat per hectare one can say that the economic treshold amounts to an average of 10 aphids (M. dirhodum + s. avenae ) per tiller.
As for the predicting model, it makes it possible to forecast the evolution of the aphid populations before they become a nuisance and hence to treat on time if they treaten to reach the economic treshold.
The data used to elaborate the predicting model come exclusively from observations in fields. They have simply consisted in counting in situ each species of aphids, the mummies of aphids killed by parasites and entomophthorales as well as the larvae of ladybirds and syrphids.
In 1987 (Latteur & Oger 1987) a first model was elaborated. The model has been actualized recently by adding the data collected during these last four years. This model groups together data collected from 1971 to 1989 in 90 winter wheat fields.
The prognosis is made shortly after flowering at the growth stage "kernel formation", which lasts 5 to 10 days (Keller & Baggiolini 1954). The first reason why it has been decided to forecast at this stage and not before, appears on table 1. The correlation between aphid populations at earing and flowering growth stages and at peak is too weak to allow to make an accurate forecast. But at the growth stage "kernel formation" this correlation is acceptable.
Tabel 1 : Correlations between the aphid populations at peak and their populations at different growth stages (19 years · 90 fields)
1 Earing Flowering Kernel Kernel formation watery ripe 1
1 0,77 0,89 i 0,12 0,35
The second reason is that, at growth stage "kernel formation", the natural enemies may already be present in sufficient numbers to play an efficient regulation role. As one can see in table 2, at this stage, the correlations between the densities of the natural specific enemies and those of aphid populations at peak are far from being negligible except for ladybirds which have very rarely played an important role in the observed fields. - 16 -
Table 2. correlation between the aphid populations at peak and the density of their specific enemies at the growth stage "kernel formation• (19 years - 90 fields).
Mummies of Larvae of l Parasitoids Entomophthorales coccinellids Syrphids
2 i -0,53 -0,3 -0,04 -0,28
The third reason is that the aphid populations are always too insignificant at growth stage "kerne! formation" to be harmful to the yield even if they may exceed the economic treshold later (Latteur & Oger, 1987).
At last, the fourth reason lies in the fact that from that growth stage on, the cereal is less likely to be infected by aphids. So a possible aphicide treatment protects it from any further reinfestation which is not neccessarily true before kernel formation. The model can be used 1°) for a general prognosis (general model) valid for all the observed fields and by extrapolation for all the fields of a whole area 2°) for one field in particular (individual model).
Equation of the general model.
log (NBMAX+l) = 1,364+0,734 log (NBM+l) -0,0064 PARM-0,0625 log (NBMYCM+l)-0,0573 SYRM. R2 (adj.) = 63,9 i
Eguation of the individual model
log (NBMAX+l) = 0,918+0,222 log (NB+l)+0,668 log (NBM+l)-0,0031 PAR-0,0023 MYC-0,0142 SYR R2 (adj.) = 62,7 %
NBMAX number of aphids (S. avenae + M. dirhodum ) per 100 tillers at peak.
NBM geometrical mean of the number of aphids per 100 tillers observed in the fields.
NB number of aphids per 100 tillers observed in the field. - 17 -
PARM average number of rnummies of parasitoids per 100 aphids
NBMYCM average number of rnummies of aphids killed by fungi per 100 aphids
SYRM average nurnber of larvae of syrphids per 100 aphids
PAR, MYC and SYR nurnber of rnurnrnies of parasitoides, of rnurnrnies of aphids killed by fungi and of larvae of syrphids per 100 aphids.
It is noteworthy that the equation of the individual rnodel includes the geornetrical rnean of the nurnber of aphids recorded in all the observation fields in order to take the general tendancy of the aphid dynarnics into account.
2.2. Importance of the natural enemies in the forecast
As far as the natural enernies are concerned, we have tried to evalua te, in the individual rnodel, the increase in accuracy brought by the data concerning the parasitoids, the entornophtorales and the larvae of syrphids, which are in general the rnain auxiliairies (table 2). The answer lies in the cornparison of tables 3 and 4.
Table 3 gives the nurnber of right and wrong prognosis (in a circle) which are rnade when natural enernies are llQ!. taken into account. Table 4, on the contrary, indicates the nurnber of right and wrong prognoses when the natural enernies are taken into accoun t.
Table 3 : Prognosis rnade without taking the parasitoids, the entornophthorales and the larvae of syrphids into account : nurnber of right and wrong O prognosis.
Nurnber of aphids Nurnber of fields for which the prognosis is : observed at peak < 10 10
< 10 61 G)
i 10 0 17 - 18 -
Table 4 Progndsis made by taking the parasitoids, the entomophthorales ahd the larvae of syrphids into account : number of right and wrong o prognosis.
Number of aphids Number of fields for which the 1 prognosis is : 1 observed at peak < 10 ) 10 1 1 < 10 61 0 i1 > 10 20 1 © 1
lh the first case (when natural enemies are not iriclude), one can notice that, if the true number of aphids observed at peak is inferior to 10, the model gives 61 right prognoses ahd 3 wrong ones. On the contrary, if the true peak is superior to 10, there are 17 right prognoses and 9 wrong ones.
If the model takes natural enemies into account, the number of wrong prognoses wh.en · the true m.imber of ' aphids a t peak i s inferior to 10 remains egual to 3. On the other hand, when the true peak is superior to 10, the number of wrong prognoses is 6 instead of 9 which shows clearly that it is important to take the natural enemies into account.
3. Dynaaics of aphid popul.ations and coabarison with the general. forecasting peak in solli.e spec:i.fic years.
The resul ts (figures n° i to n° 11) relate to the 11 years (1972, 73, 80 to 83 and 85 to 89) for which there were observation data in at least 5 fields. The figures acl.so show .:.
1. - the number of aphids forecast at peak (Prog. = .. aph/til.) ;
2.- the forecast moment (the arrow) which is also that of the growth stage "kernel formation";
3.- the number of degree days superior to 10 degrees [which is according to Carter & al, (1982) the physiological zero of s. avenae ) and, between brackets, the normal degree days. - 19 -
20 -• 15
C:" " lli. 10 e -i 0 ,c: 5 .!::; ::i:
25 31 5 10 15 20 25 30 5 MAY JUN
56 ( 911 89 11521 150 (236) 225 (335) Degree doys > 10 •c (normal J
..,.. 15 '.e ..Q. C, 2 10 ..• ·e E 5 :, :::t
0 - Aphidiids
..,.. 1..1. 0 - .o,5 a �> ....a
- Coccinellids c::::J Syrphids
Fig.l. Average density of aphids and their specific enemies in 7 winter wheat fields in 1972. - 20 -'-
20
' • 15 ".. .."'• c,j. 10 e .g 0 5 -!::... t
25 31 5 10 15 20 25 30 5 15 20 MAV JUN JUL 1 1 1 1 1 1 77 191) 132 11521 246 1236) 361 (335) Degree days > 10 •c I normal)
.. 15 :.:,, ..a 0 � 10 • ·eE 5 :, :::i:
0
:o,s a > _,:;
- Coccinellids c::::::J Syrphids
Fig.2. Average density of aphids and their specific enemies in 9 winter wheat fields in 1973. - 21 -
20 �- ...... 15 C:" ..,. a .,;. 10 e
0 5 -!:: �
25 31 5 10 15 20 25 30 5 10 15 MAY JUN JUL 1 1 1 1 1 1 65 ( 911 136 1152) 183 (236) 236 (335) Degree d11ys > 10 •c ( nor m11ll
„ 15 :c... a... 2 10 • ·e e:, s ::t:
- Aphidiids ..... �1,0 a 0 ....e • o,s a > a� ..J
- Coccinellids c:::J Syrphids
Fig.3. Average density of aphids and their specific enemies in 6 winter wheat fields in 1980. - 22 -
20
... 15 ".. .."' ..;.. 10
25 31 5 10 MAY 1 1 1 1 1 152 (911 - 246 (1521 284 (236) 395 (335) Degree days > -10 •c ( normal)
15 ...... � "G. C, 2 10 •.. ·eE 5 :, :::i:
0
...... i" 1.o C, 2 ...• o,5 >" ..,:;
„ Coccinellids t::J Syrphids
Fig.4. Average density of aphids and their specific enemies in 10 winter wheat fields in 1981. - 23 -
20 � .!
15 " "..,. ..; 10
E
0 5 -!:: � 0 25 31 5 10 15 20 25 30 5 10 15 20 25 MAY JUN JUL 1 1 1 1 1 1 104 (91) 215 1152) 292 (236) 423 (335) Oegree doys > 10 •c ( nor mall
.... 15 :c... a 0 2 10 .. ·e. E 5 ::, X
0
...VI ::_ 1,0 a 0 2 - ...o.s .J:;
- Coccinellids CJ Syrphids
Fig.5. Average density of aphids and their specific enemies in 8 winter wheat fields in 1982. - 24 -
20
' 1 "• 5 •" ".. .,; 10
25 31 MAY 1 1 1 1 39 (911 125 (1!12) 212 (236) 359 (335) Degru d11ys > 10 °C (norm11ll
• 15 :c... "Q. 2 10 • ·e 5 e:, ::t
...• {1,0 a C) ....5! • o,5 "> ...i;
- Coccinellids
Fig:6• Average density of aphids and their specific enemies in 7 winter wheat fields in 1983. - 25 -
20 =.! "• 15 •r: "� c,j 10 e :, "t, 0 s -!:: "t, ;: 0
25 10 15 20 25 30 MAY JUN 1 1 1 1 1 116 (911 177 (152) 223 (2361 323 1335) Degree days > 10 •c ( normal l
..,.. 15 '.c Q.... 0 2 10 .. "iE E 5 :::, :X
o - Aphidiids
..,.. =:_1,0 a 0 2 ::o.s >" ..."
Im Coccineltids c:J Syrphids
Fig.7. Average density of aphids and their specific enemies in 8 winter wheat fields in 1985. - 26 -
20
.._• 15 .,.. .."'• lli. 10 e i a 5 .!,: t
25 31 5 10 15 20 25 30 25 MAY JUN 1 1 1 1 1 1 1 91 (911 1'5 (1521 2'73 (2361 372 (3351 Degru days > ID •c (normal)
15 ..,.. :c ..A. C, S! 10 .• eE 5 ::, %
0 - Aphidiids c:::J Entomophthorales ..,.. ::,..,, o C, ....S! ..• o.s ....1:;
- Caccinellids c:::J Syrphids
Fig.8. Average density of aphids and their specific enemies in 7 winter wheat fields in 1986. - 27 -
- 20 !!- - 15 "..a ,... a .,;. 10 e i 0 5 .!:, "tl t
25 31 5 MAY 1 1 1 1 1 1 78 ( 911 115 (1521 184 (236) 292 (335) Oegree days > 10 •c l normall
„ 15 �.., "a. ; 10 ..• . E E 5 ::, ::t:
- Aphidiids
..,.. 1,0 fa �0 -.o,s > �:;
- Coccinellids CJ Syrphids
Fig,9, Average density of aphids and their specific enemies in 7 winter wheat fields in 1987. - 28 -
20 .!
- • i5 ".. ,...• ,.; 10 e .: 0 5
�
31 5 10 15 20 5 10 15 20 25 25 JUN 25 30 JUL MAY 1 1 1 1 1 1 132 (911 181 (152) 258 (236) 336 (335) Degree days > 10 •c I normal l
...„ 1 5 :.;..... § 10 •.. ·e e 5 :, :::t:
- Aphidiids c:J Entomophthora.1u ..... f..1. o �C, - .o,s "> _,:;
- Coccinellids c:J Syrphids
Fig.10. Average density of aphids and their specific enemies in 5 winter wheat fields in 1988. - 29 -
20
.!!
' 1S •a •r: a� c,i 10
E b 0 s -!:: b � 0 25 31 5 10 15 20 25 30 s 10 15 20 25 MAY JUN JUL 1 1 1 1 1 13S (911 183 (1521 278 (2361 38, (335) Degree dc,ys > 10 •c ( normc,IJ
.. 1S '.., a... 0 S! 10 • ·e :> s :::i:
0 - Aphidiids c::::J Entomophthorc,les
..,.. 11.0 a 0 5? :o,s >" h ...,a
- Coccinellids c::::J Syrphids
Fig.11. Average density of aphids and their specific enemies in 6 winter wheat fields in 1989. - 30 -
3 .1. Winter... influence
The earliest development of aphid populations was observed by the end of May after the mildest winters (1988 and 89) (Table 5) whereas the latest one occurred about June 15 - 20th and came after the harshest winters (1985, 86, 87) even when spring was rather warm as in 1985.
In the course of 11 years as related here, the average aphid populations in the experimental fields have definitely outnumbered 4 times (in 1972, 80, 81, 85) the economic treshold of an average of 10 aphids per tiller. There have been quite mild winters during the first two years, a normal one in 1981 and a cold one in 1985. The seven years during which the aphid development was inferior to the economic treshold have never recorded popula tions superior to 5 aphids per tiller _ There have been mild, normal or harsh winters.
These observations seem to prove that if the rigour of winter has an influence on the precocity of the arrival of aphid populations in the wheat fields, it does not influence the importance of the latter in the good season.
Table 5 : Number of days for which the minimum temperature is inferior to 0° C, - 5° C, - 10° C, - 15 ° C, and - 20° C during the winter months (December, January, February, March).
//III/III Nurrber of d""" for which the rninimum t...... ,..=ture is
1 Year < 0° C < _ 50 C < -10° C k -15° C < -20° C 1 1972 43 (") 6 2 0 0 1973 62 6 0 0 0 l 1 1980 43 10 0 0 0 1 1981 60 11 0 0 0 1 1982 67 17 6 3 1 1 1983 53 12 0 0 0 1 1985 70 28 23 7 0 1 1986 68 32 13 2 0 1 1987 70 32 7 2 0 1 1988 38 5 0 0 0 1 1 1989 23 0 0 0 0 (") normal number 56
3. 2. Influence... of ... temP eratures ... in ...June ... -....Ju )._y.
We have already observed (Latteur, 1989) that the correlation coefficient referring to the number of aphids ( S; avenae or M. dirhodum ) at their peak and to the ternperatures in June is definitely negative. This is confirmed by the obs·ervation of - 31 -
the results of these 11 years, namely if one compares the 1972 results with those obtained in 1982. Indeed, while the aphid density and that of their specific enemies were quite similar by 15th June, the aphids reached a maximum average number of 17 in 1972 and of 4 in 1982 while the number of degree days superior to 10° C from 15th June to 15th July was far weaker in 1972 (136) than in 1982 (208). However, 1972 is also different from 1982 because of populations of less important predators larvae after 15th June and because of a less early cereal growth stage (stage "kernel formation" observed on 25 th June in 1972 and 16th June in 1982), two factors which may have been more important than the temperature on the evolution of aphid populations.
3. 3. The___ s_pec;i.fic ___ e 1wm;ies
The specific enemies are not the only regulation biotic factors of cereal aphids. The polyphagous predators (carabidae, staphylinidae and araneae ) that are not recorded in this study may also play a non-negligible limitation part (Vickerman & Wratten, 1979; Sunderland & al., 1986). Moreover, the phenology of the cereal may influence the multiplication rate of aphids. The whole of these biotic and abiotic factors makes the comprehension of the dynamics of aphid populations very difficult. The statistical analysis of the data (eh. 2) though, has enabled us to evaluate the average relative importance of each of the specific enemies, which is a first step to the quantification of their action.
Besides, one will note that all the years with weak aphid populations (5 5 aphids/tiller) have in common the fact that at least one specific enemy is observed from the appearance of aphids on and often maintains itself at a relatively high level during the whole development of aphid populations : parasitoids in 1973, 88 and 89, syrphids in 1982 and 86, parasitoids and entomophthorales in 1983 and at last parasitoids and syrphids in 1987. On the contrary, the years of outbreak (� 15 aphids per tiller) go together with sporadic and rather weak presence of specific enemies except in 1981 when entomophthorales, parasitoids and syrphids were to be found, at rather weak levels however, during almost the whole development of aphid populations, without any decrease in the density of the latter before the beginning of July.
Rabasse and Dedryver (1982) relate that parasitoids of cereal aphids may multiply during mild winters in the French Brittany on anholocyclic forms of these aphids, which enables them to be often present in spring in numbers allowing them to play a significant regulation role.
This behaviour seems tobe the same in our regions too, as :
1° ) a rather great density of mummified aphids w.;c� observed in 1988 and 1989 after a very mild winter and in 1983 after a moderate one winter as soon as the aphids appeared in wheats by - 32 -
the end of May (1988 and 89)-beginning of June (1983) and they seem to have played an important regulation role ;
2° ) during the harsh 1982, 85, 86 winters aphidiid mummies were not observed in wheats (1985 and 1986) or appeared very late, by the beginning of July (1982).
We have observed however that, after the harsh 1987 winter, mummies of parasites appeared in rather important numbers as soon as the aphids had colonized the wheats. This might be the result of the fact that, during some years, these parasites can also winter in diapause and so, be quite frost·proof.
The entomophthorales have been recorded at least once every year during the observation except in 1985, 86, 87, that is after the harshest winters and for unknown reasons. When they are present, it is in a more sporadic way than the parasites, except in 1981 and 83, when they were observed continuously. Their maximum development is observed when the aphid starts decreasing or shortly after it. Their importance, however, does not seem to depend exclusively on that of aphid populations as we observed twice, in 1988 and 89, about 8 % of mummified aphids · that is quite a lot · in weak aphid populations (from 1 to 2 aphids/tiller).
Syrphid larvae have been recorded in the aphid populations at least once a year. The importance of their density does not seem to be influenced by the harshness of the winter. These predators are often observed in weak aphid populations (an average of 1 aphid/tiller). They are almost as frequent as the aphidiides but they appear a bit later, at the earliest by the beginning of June instead of the end of May, like the parasites. When the aphid populations are increasing, their density can reach 0,7 larva for 100 aphids.
Ladybird larvae are the least frequently observed among the specific enemies. They have only been recorded during 3 years (1973, 82, 86) out of 11 and their densities have not exceeded 0,2 larva for 100 aphids.
Larvae and adults of chrysopids have rarely been observed and anyway in too weak quantities to be recorded in our results.
3. 4 . compqrison .. of.. the .. 9'ilneral. forecas ting___ peaks... wj._th . those obs(;lrved..
By comparing, in figures 1 to 11, the average maximum number of aphids forecast by the general model at growth stage "kernel formation" and that really reached by the populations, the precision of the model can be evaluated.
So, it appears chat the average r,c:mber of aphids forecast is superior to that observed in 198 3, 86, 89, is similar in 1982 and 88, and is inferior in 1972, 73, 80, 81, 85 et 87. - 33 -
The general model seems to underestimate more often than i t overestimates, which is probably regrettable for farmers as we think it better to advise a treatment unnecessarily than the contrary.
However, the main thing is to advise accurately in connection with the economic treshold. It is thus reassuring to notice that when the latter amounts to an average of 10 aphids/tiller the advise to treat or not to treat has proved inadequate only 1 year (1985) out of 11. Moreover, this good counsel would be right even if the treshold were, for economic reasons, reduced up to 5 aphids/tiller, which is still more reassuring.
4. conclusions.
As a conclusion, it is important to point out that within 20 years of field observations on cereal aphids, we have not met twice the same situation. Figures 1 to 11 are a good illustration of that great variability.
The number of factors influencing the dynamics of aphid populations is often so large that it is difficult to identify the true causes of the evolution observed except in very rare cases such as the nearly absolute absence of bene·fical organisms in 1985 or the dominance of parasitoids in 1989.
It is the reason why the field biologist who wants to forecast the development of aphid populations with a maximum of accuracy must admi t that dynamic or regression models have become unavoidable tools.
5. Bibliography
CARTER, N. DIXON, A.F.G. & RABBINGE, R. 1982. Cereal aphid populations : biology, simulation and prediction. Wageningen . Centre for Agricultural Publishing and Documentation : 1 - 91.
FOUGEROUX, A. 1990. Les ravageurs du ble d'hiver au printemps. Phytoma, 4/6 : 47-50.
KELLER, Chr. & BAGGIOLINI, M. 1954. Les stades repreres dans la vegetation du ble. Revue Romande d'Agriculture de Viticulture et d'Arboriculture, 10, 3 : 17-20. - 34 -
LATTEUR, G. 1989. Pucerons : Epidemiologie et prognose. Application aux pucerons des froments d'hiver, des betteraves et des plants de pommes de terre en Grande Bretagne, en France et en Belgique. "Euraphid" network : Trapping and aphid prognosis. Edited by R. Cavalloro. C.E.C. Eur. 11.559 : 131-148.
LATTEUR, G. & OGER, R. 1987. Principes de base du systeme d'avertissement relatif a la lutte contre les pucerons des froments d'hiver en Belgique. Annales A.N.P.P., 6, II/III : 129·136.
RABASSE, J.M. & DEDRYVER, C.A. 1982. OVerwintering of primary parasites and hyperparasites of cereal aphids in Western France. Aphid Antagonists . Edited by A.A. Balkema, Rotterdam : 57-64.
RIJSDIJK, F.H., LEEUWEN-PANNEKOEK, I., RABBINGE, R. & ZADOKS, J,C. 1981. EPIPRE, een begeleidingssysteem voor bestrijding van ziekten en plagen in wintertarwe. Gewasbescherming, 12 (1) 10.
SUNDERLAND, K. D., FRASER, A.M. & DIXON, A. F. G. 1986. Field and laboratory studies on money spiders (Limyphiidae) as predators of cereal aphids. Journal of Applied Ecology, 23 : 433-447.
VICKERMAN, G.P. & WRATTEN, S.D. 1979. The biology and pest status of cereal aphids (Hemiptera Aphididae) in Europe a review. Bull. ent. Res. 69 : 1·32.
WRATTEN, S., MANN, B. & WATT, A. 1987. Un systeme d'aide par ordinateur pour le controle des pucerons des cereales et des ravageurs du colza. Annales A.N.P.P., 6, I/III : 53·63. - 35 -
A model-based catalogue of case studies as a tool for decision making in the control of the cereal aphid Macrosiphum [Sitobion] avenae in winter wheat
by F. HOLZ
Martin-Luther-Universität Halle-Wittenberg, Sektion Pflanzenproduktion, Lehrstuhl Phytopathologie und Pflanzenschutz, Ludwig-Wucherer-Straße 2, 4020 Halle (S.) (G.D,R.)
Introduction
The forecast of population dynamics of Macrosiphum [Sitobion] avenae is complicated because the increase of abundance from tillering up to the milky ripe of wheat is influenced by numerous driving variables. By this reason several control thresholds were recommended by different authors in the past. WETZEL and FREIER proposed already 1975 as &eshold 3 to 5 aphids per ear to the time end of flowering/begin of milky ripe. This control threshold is used until nowadays in the G.D.R. and it represents a good help for decision making, But the flexibili ty of such tools is restricted. Therefore a simulation model was developed for the population dynamics of M. avenae.
The model
The model was created by FREIER (1983) and validated by HOLZ (1986), PESTSIM-MAC is the short name of the model. It is based on the concept of SONCHES, a �imulator Qf Honlinear �omplex flierarchic IcoQystems (KNIJNENBURG et al., 1984). This simulator includes tools for the building, evaluation and application of models of ecosystems. SONCHES is a branch specific simulation system for the design of dynamical, explaining, modular, time- and space-discrete, flexible models. SONCHES is written in FORTRAN IV and it works under - 36 -
T,L,BLE l
ClhlailJ'a1
input variable case value remarks
weather warm and dry 19·c: 13.5mm average value of dai!y mean ° normal 16 C; 29.1mm temperatures and sum of coid and wet 15·c; !3(:.1mm precipitation in the period DC 60-78 .-.,,: parasÜ'ation iow 2% percentage ot mummified aphids midd!e 8'% in relation to the whole high 20% aphid popu/a tion 2 number of predator units / m abundance of low 1 predator unit = 1 adult ladybird predators middle 5 or 2 larvae of ladybird:;, high 15 hoverflies or lacewings
age structure young 13% percentage of adults of aphid normal 20% {winged a nd 1;m1ringed) population old 26% in lhe aphid population
TABLE r·1 C@mmenndg1JIDile tll:rnr��lhl@ld� (iw,Jm1��/ze�1d f@r ffftdd=irtil@lt�d ded�i®!Iil milldlfil! hn Unt t@Ililttrr@Il (lJ)1f M�ttl'@sip!JJJrtlllßlfJ. {§Jd@bJ!@I!11]JJVtJJDiUJ fillil wfiiiteir wlhl®ait tt@ 01® �tige IDJCC �\-).0... /. / Y 's· ( ·,.. "---�,/�;:- young normal old young normal old young normal old 0 ') low 1,0 i,1 1;1 1,3 1,4 1.5 '-• '- 2.3 1.6 2,4 low middle 1.4 1,5 2,() 3,2 3,4 3.5 high 3,C 3,3 4,0 4,3 4,6 0,,- 1 5,8 7i - 3,2 6,3 ... CD i: Q. low 1.7 1.6 1.5 2,4 2.2 2.0 4,1 J.7 J.4 � middle ö middle 2,4 2 . .3 2. 1 3.� 3.3 3.i 5.':l 5.3 4,9 Q 1 7 - ·;; high 5:�} 4,6 4,4 ').� (,.4 6,2 ....,,, 7,1 ',j • C es... • 0. "" low J.J 2.? 2.1 5.G 4 1 3.1 5.3 high middle 4,8 4.'.) 3.1 7.4 high ·:J/: .37 7,:)* 3,3 3,2 - 37 - the operating systems VAX and MSDOS. PESTSIM-MAC describes the development of the aphid population from the beginning of immigration into the wheat stand in spring up to the decline. It co nsiders the most important driving forces like weather, parasites, predators and condition of host plant. Model structure and process algorithms are explained by ROSSBERG et al. (1986). Why was such an extended model constructed? The security and accuracy of control thresholds seems in sufficient as mentioned. Secondly investigations of control strategies and hypothesis about real processes are possible which can't be tested in laboratory or under controlled conditions. Moreover a model of this type integrates knowledge from various sources. In this way a memory is created which also may contain so-called soft data. The discovering of gaps in knowledge is one important result of such an abstraction by a model. The possibilities for application of a well-structured and validated( ! ) model on practical purposes depends on several factors like quality of the model, complexity and handling of model, technical conditions and others. An on-line and problem-oriented application by the final user appears as the best and easiest way. Unfortunately PESTSIM-MAC is too complex and time-consuming for an on-line or an individual usage by the farmer or by the plant protection specialist. So there is the demand of searching for a quite easy form of application. The idea of a catalogue of case studies could solve this problem. The catalogue of case studies The basic assumption is that the abundance dynamics of a pest are determined to a large scale by only few driving factors. These key factors should have some typical manners of behaviour durin g a couple of years. So i t would be possible maki ng simulation studies for various constellations of such typical cases of the dynamics of certain variables. The head line for this investigations could be "What happens, if ... ?". - 38 - --, T1 /-,\·\B''L, .. : L.:::: -�' JEw-�ltm@tUm\ii. @!I Une control threshold real abundances year place variety selected from catalogue DC 69 maximum '1980 Peißen .A.!cedo 1.4 0.3 5.2 1981 Peißen ,ll,icedc 6.8 0.1 0.6 1982 Peißen •Jcedo 1.1 t1 10.0 l 1984 Pe1ßen 1'.\lcedo 10 C.1 3.7 Taras 1.0 1.3 11.0 l Schneliroda Fakon 1.1 t·-' 1.2 1.1 0.1 1.4 Taras [aphlds/ear] 1985 Peißen .o.icedo 2.2 0.2 1.5 Schnellroda Alcedo 2.2 G.1 0.9 Reg1na 2.3 0 1.4 Fal,on 2.3 0 0.4 1986 Pe,ßen Alcedo 1.1 0.5 2.4 Schnellroda Galahad 1.1 1.9 insec1icide used 1 1987 Peißen Alcedo 1.3 0.3 1.0 1988 Peißen Alcedo 1.3 0.6 1.8 1989 Peißen Borenos 7.8 2.4 * 2.4 - 39 - Weather, parasitation rate, abundance of predators and age structure of aphid population were choosed as variables for the case studies with PESTSIM-MAC. lt seems enough if there are considered three cases of typical behaviour for every variable in relation to the development of aphid population: best, normal and warst case. At last that means 3 4 = 81 imaginable constellations. An important problem is the providing of suitable data. The use of pure artificial data is questionable. Therefore the author created "synthetic data with a real background". What does it mean? The long-period average dynamics of every selected variable were defined as "normal case". Then the rows of data were constructed by the combination of fit segments from real data sets. The data material for "best case" and "warst case" was put together in the same way. Table 1 supplies an overview of characteristics of driving variables. Now the model computings were made on this data base. The results of simulations are not fixed values but population curves because PESTSIM-MAC is a dynamical model. So it would be possible giving a forecast of abundance dynamics up from every date. But the restricting fact is the uncertainty of prognosis of driving forces (especially weather). On the other band it is more easy usini fixed values to a fixed date in practice. So only the short intervall between DC 69 and DC 73 is favourable for decision making to control M. avenae. Therefore the results of case studies are presented for the end of flowering stage of winter wheat ( DC 69) as the right moment for decision making ( table 2). Every number in table 2 embodies a threshold. A significiant damage has to be expected if the selected level is reached or passed. The thresholds are valid for an expected yield of 60 to 70 dt/ha. If higher yields are expected a small reduction of table value is recommended. Following general findings are detectable from the case studies: - The threshold of the "total normal case" (i.e. all driving variables show their "normal" dynamics) is situated exactly - 40 - in the intervall of the mentioned control threshold of WETZEL and FREIER ( 1975). So both thresholds confirm each other. - The scope is much greater for decision making by the catalogue than by control threshold. Moreover the catalogue allows a real quantitative forecast in opposite to the control threshold which is a kind of negative (=indirect) prognosis. - The catalogue permits taking account to the most important driving factors in well-graded steps. The following relation-shape shows the relative importance of each driving force in comparison to the others: weather parasitation predators >> age structure. The conclusion= is that there= is no necessity of noticing the age structure of aphid population in practice. So it is recommended that the case "normal age structure" should be used normally. - Numbers marked by "*" (table 2) show a very interesting fact. In this cases the abundance has reached or even passed their maximum to this early time. This sentence supports the hypothesis that antagonists are able to regulate the aphid population development below the economic threshold if the enemies appear early and in a great number. That demands an involving of the abundance of predators and the parasitation rate into the supervising and decision making. The catalogue was tested by an application on real data. Provided that the assumption is right that a significant damage is caused if the abundance maximum reachs 10 or more aphids/ear the catalogue would have recommended right decisions in all tested cases as the results illustrate ( table 3). Al though the abundance reached only four times a dangerous level the security and accuracy is quite good. The data from 1989 (marked by "*") supply an important evidence. Already to the end of flowering has the abundance reached - 41 - their maximum. This soon decline was caused by enemies. Easy can the catalogue be handled in the proposed manner if it is simplified by removing the cases "young" and "old" age structure. So the catalogue could be a real alternative to the control threshold. A further improvement of catalogue is imaginable. Following factors could be involved: differences of wheat varieties in resistance (in widest sense) against aphid infestation, - expected yield, length of period of milky ripe of winter wheat which is most important for the extent of damage caused by aphids, - other control strategies. Moreover it should be proved if a computer-based decision program is needed (for example as a part of a management system). References FREIER, B. (1983) Untersuchungen zur Struktur von Populationen und zum Massenwechsel von Schadinsekten des Getreides als Grundlage für ihre Uberwachung, Prognose und gezielte Bekämpfung sowie für die Entwicklung von Simulations modellen. Halle-Wittenberg, Martin-Luther-Univ., Dias. B, 246 PP• HOLZ, F. (1986) Einschätzung, Vervollkommnung und Nutzung von Simulationsmodellen für die Populationsdynamik von Schad insekten des Getreides, dargestellt am Beispiel der Getreidelaus ( Macrosiphum avenae [ Fabr.]), Halle Wittenberg, Martin-Luther-Univ., Diss., 99 pp. KNIJNENBURG,A., MATTHÄUS,E. & WENZEL,V. (1984) Concept and usage of the interactive simulation system for ecosystems SONCHES. Ecological Modelling 26, 51-76. ROSSBERG, D., HOLZ, F., FREIER, B. & WENZEL, V. (1986) PESTSIM-MAC. A model for simulation of Macrosiphum avenae FABR. populations. Tagungsberichte der Aka demie der Landwirtschaftswissenschaften der DDR 242, 87-100. WETZEL, Th. & FREIER, B. (1975) Kenntnis der Vermehrungspotenz und des Massenwechsels von Getreideblattläu sen als Voraussetzung zur Prognose und gezielten Bekämpfung. Archiv für Phytopathologie und Pflanzenschutz 11, 133-152. :::- _4.2 - ON THE OCCURENCE AND CONTROLOF INSECT PESTS AFFECTINGWINTER WHEAT EARSIN PRACTICE ChristaVOLKMAR (*) and Th. WETZEL(*) (*) ,Martin-Luther-Universität Halle-Wittenberg, Landwirtschaftliche Facultät, Institut für Phytomedizin, Ludwig-Wucherer-Straße 2, HALLE/SAALE 0-4020 F.R.G. SUMMARY '''98sr Analysis of the occurence of insect pests affecting winter wheat ears and ofthe scale ofdamage revealed cereal aphids and wheat midges to be capable of gradation in hlgh intensitygrain production in the district ofHalle. The Thysanoptera affecting cereals continue to be latent pest.s doing hann to winter wheat. The optimal dates for control of wheat midges and cereal aphids are reached at different stages of plant development. After the threshold value has been exceeded, Contarinia triticd:K:\rby) is reliabiy· controlled at the begin of ear emergence (DC 50 to DC�fi3) and Macrosiphum avenae (Fahr.) at the end ofwinter wheat flowering (DC 68 to DC 70). Carefully directed treatment of one insect pest influences also the development of the populations of other insect pests that affect t..lie ears. These interactions should be considered when drawing up decisions for control action. INTRODUCTION In recent years several statements were made about the significance ofa purposeful application of chemical agents against cereal pests in the framework ofintegrated pest cöntrol (WETZEL, 1983; WETZEL and SPAAR, 1965). In this - 43 - connection special att.ention has been given to the control of the agroecosystem and its responseto chemical agents. In order to avoid arbitrary and routine applications of chemicals, it is necessary to monitorthe incidence of different pest species in winter wheat crops and to investigate the economical and ecological benefits of integrated control measures in a large-scale trial. When doing so, all activities must be directed on the cereal plant and the reliability by yield and quality. Pest control is supposed to interfere as a kind of regulator into the population structure of one or more pest species,ü othermeasures, especially crop and soll cultivation, cannot avoid a gradation of thepest and the involvedyield losses. Theaim of the production trial carried out between 1983 and 1987 was to study the eft'ect of the insecticides metamidophos and . dimethoate on the population development of ear pests in winter wheat crops under naturally difl'erentiated conditions of incidence and, furthermore, to giverecommendations for a purpoaeful practicing of plant protection measures. The experiments were orientated on a combined incidence of the ear pests : cereal aphids, wheat midge andcereal thrips. METIIODS The experiments were established in the cooperative farm for crop production Barnstädt, Halle district. The test fields covered an area of to 100 hectares, their lengthbeing ahout 500 metres.Chemicals were applied in stripes by means of ground machinery using the resulting pass-ways. The two test variants were untreated and treated stripes. Each passage or stripe represented one test plot. In 1983 the field scoring was done on 5 locations of each passage from which 25 plants were evaluated. 50 ears per passage were analysed in the laboratory. In 1984 to 1987 the sizeof samples for visualassessment amounted to 60 earsper passage. Thenumber of laboratoryanalyses in 1984 and 1985 was 60 ears per variantand decreased to 30 ears in 1986 and 1987. In all test years the investigations startedwith the first scoring of the area at ear emergence. Thus, the actual concentration of pests was to be determined, together with the degree of homogenity. The first directed control measure was taken at DC 52 to 56. In the years 1983 and 1987 methamidophos (Filitox) was applied. The second application was given at the end of O:owering (DC 65 to 69). In the years 1983, 1984 and 1986 dimethoate (BI 58 EC) was used. After spraying the field was scored at DC 68 to 70 and DC 75 to 78 to obtain information about the population development of - 44 - 3 A C - 50 40 - 30 1 - - 20 - 10 �'-- ...... � �'-- 0 0 [b [b [b ----- K-B KB KB KB K B KB KB KB -1983 1984 1985 1986 1983 1984 1985 1986 Figure 1 : Contarina tritici : numbe1sof damaged grains (A) and percentages of infested ears (C) in controls (K) and treated plots by methamidophos (B) at DC 50-56. t------·-- rm--[jjj-o11- K B K. B K B K B K B 198 3 1984 1985 1986 19 8 7 Figure 2 : Sitobion avenae : numbers of aphids/ear for control (K) and treated plots by methamidophos (B) at DC 50-56 (1 - 2 - 3, successive sampling dates). - 45 - the ear pests in both variants. The yields of the chemically treated plots were compared with data from other test plots and combine-harvested areas. The statistical evaluation was made on the basis of the variance analysis together with theMaximum-Modulus test. RESULTS The first control measure was aimed at studying the possibilities for taking direct influence on the combined incidence of wheat blossom midges and cereal thrips. The best chances for an optimal control of both insects are offered at thebeginning of ear emergence. The results of a 5-year test series allow to statethat even when the current threshold values for Contarinia tritici (Kirby) were observed, yield losses could not always be avoided. Therefore we propose to correct the threshold values forcontrol measures against thewheat blossom midge. Visual examination : 1 ovipositing femaleper 1 to 3 at DC 51 to 54 Sweep net capturing: more than 50 females per standard capture at DC 51 to 54. Terms for the abundance assessment: calm warm weather, best time 20 to 21 hour; As revealed by the data analysis, in the years of 1983 to 1985 the attack by wheat blossom midges was rather low (less than 1 damaged grain per ear) (Fig. 1). Averaging all test years, we recorded an efficiency of 48.0 and 39.3 % respectively for the criteria "damaged grains per ear" and "attacked ears". In 1986 however, we were confronted with the urgency to control wheat midges effectively. The average of 2.1 damaged syncarpies per ear signalized yield losses of about 5 % in view of a general yield potential of 7 t per hectare. Spraying at the date of ear emergence (DC 55 to 56) did not reduce the number of damaged grains per ear, of larvae per ear and of larvae attacking syncarpies. Since no data were recorded on the flight dynamics of C. tritici, we can suggest that there was no good coincidence between the date of insecticide application and the moment of the main flight of wheat midges. Literature studies have shown that our time of spraying (DC 55 to 56) was too late for preventing the egg-laying of the predominant species C. tritici (BASEDOW, 1975; LÜBKE, 1982). Another explanation is given by KÖRNER et al. (1984). They recommend to apply methamidophos in dry and hot weather in the evening hours with the double quantity of water in order to guarantee an effect of the - 46 - 6 5 A T 4 3 ·2 0 JJJJ K B K B K B 4 3 _9_8_4 _ ___.__ l_ 98_6_, __ 1_9_fJ...:3:...__L__1_s__ 8 _ _L __1_ s_8_6_--''----1 _9 _8_ _...,...... __ 1 Figure 3 : numbers of aphids (A) and thrips (T) per ear in controls (K) and in treated plots by dimethoate (B) at DC 65-68 (1 - 2 - 3, successive sampling dates). A C 340 333 340. 333 4 So 3 1 4o 1 1 3o 2 1 1 2o 1o .[b: [b KB K B K B 1984 1986 19 1983 83 1964 1986 Figure 4 : numbers of damaged grains per ear (A) and percentages of infested ears (C) by Contarina tritici in controls (K) and treated plots by dimethoate (B) at DC 60-65. - 47 - treatment. This was not considered when spraying in 1986. The insufficient effect of metamidophos in that year underlines the demand that the question of taking control measures against wheat midges should be decided for each field separately at the beginning ofear emergence with regard to the threshold values. In all experimental years wheat midges occurred rather poorly (less than 3 insects per ear). A treatment at the beginning of ear emergence helped to reduce the abundance level persistently. Even in the phase of milky ripeness the mean effect of this application variant was still 34.4 %. Significant yield losses are not provable for therecorded abundance values. In none of the experimental years we had to interfere into the population development ofthe midges by use ofinsecticides. Aphid populations were controlable both in case of low and medium incidence (1983 to 1985 and 1987) as well as under the conditions of gradation (1986), with metamidophos spray at ear emergence (Fig. 2). At the milky ripeness ofwinter wheat the effect was still 37 .2 % averaging the test years. In years with heavy aphid infestation we recorded during the 3rd scoring (DC 73 to 76) an effect of 88.4 % (1983) and 55.8 % (1S86). The observed reduction of abundance was in all years sufficient to keep the aphid population below the threshold values. However, when we regard directed chemical ·control steps, the mere application of metamidophos to control cereal aphid must be refused because at present it is not possible to give a reliable prognosis on the expected level of incidence at the moment of ear emergence. The analysis of the scoring at DC 50 to 59 over the 5 test years by use of interpretation and decisionaids (FREIERet al., 1982) produced clear evidence only for 1984. In that year with and average of 0.01 aphid per plant we susceeded to prevent damage by aphid attack in all cases. The lack of security of a treatment decided at the time of ear emergence is demonstrated by the results obtained for 1983. The data on the attack at DC 50 to 54 signalized a dangerous incidence of aphids under all circumstances (mean 0.5 aphids per ear and standard leaf). However, the populations developed only to a medium level thanks to unfavourable weather conditions and a high parasitation of the aphids. The data from the 2nd and 3rd scoring revealed that the chemical treatment at the end of wheat flowering could have been omitted if the economic threshold values suggested by WETZEL et al., (1987) had been observed. - 48 - In figures 3 and 4 informations are given about the effect of dimethoat on ear pests during the flowering of winter wheat. The influence of a single spray with dimethoate on cereal pests was demonstrated by the average effect of67.3 % for the three years of experiments. Under the conditions of strong gradation in 1986 the treatment cause an 82.8 % reduction ofthe infestation. Considering the ears only, the application was successful with 98.9 %. In each year of experimentation cereal aphids were reliably controlled. Abundance levels could be kept below the threshold value untilthe natural breakdownof the population. On the untreated passages ofthe variant dimethoate, thrips were recorded with 3 insects per ear only (Fig. 3). For population density a spraying of dimethoate produced a mean efficiency of 58.2 %. The results confirm that a directed application of dimethoate against aphids involves also a decrease of thrips until they leave the ears by their own. lt was suggested that the use of a systemic insecticide against cereal aphids would have influence also on the larvae of wheat midges in the infested syncarpies. The effect of a single spray on these pests was shown by several relationships. The mean efficiency for the criterion larvae per ear and damaged grains per ear was 37.2 % and 46.2 %. Thus, under the prevailing conditions of infestation one application was enough to achieve a sufficient reduction of the attack even until the end offlowering. Yield losses on the treated stripes were less than 5 %. This fact was especially interesting in the year 1986. The necessary spray against aphids reduced also sufficiently the extent of damage caused by midges (variant : 1.4 infested syncarpies per ear), whereas on the untreated stripes the insect population reached values which chemical control (on the average 4.5 damaged grains per ear, Fig. 4). Thus, plant protection experts in practice can choose between two possibilities of effective midge control. When for reasons of time or organisational problems a treatment against C. tritici is impossible at the beginning of ear emergence, the larvae population can also be influenced by spraying directly against aphids at the end of wheat flowering. Yet, this requires the application of a systemic agent, since deltamethrine given at DC 59 to 71 did not produce any effect on the hidden midge larvae. Any ideas to elaborate a combined monitoring and control strategy against ear pests in winter wheat crops are not realistic because the decisions to take direct control measures against wheat midges and cereal aphids have to be made at different times of plant development. If an insecticide is to be applied against - 49 - C. tritici after the threshold value is exceeded, it must be made sure on these fields that the spraying against aphids at DC 68 to 71 can be omitted. According to the results obtained (Fig. 2), the application of metamidophos at ear emergence caused a remarkable delay of the aphid propagation. Comprehensive yield analyses were carried out ot investigate the influence of ear pests on the yield characters of winter wheat. The poor infestation by all pests which were studied in 1984, 1985 and 1987 revealed yield differences between treated and untreated stripes of more accidental character. In 1983, however, aphids caused greater damage. Wheat midges and thrips did not occur in such abundances that they had to be controlled. These circumstances elucidated significant yield differences between treated and untreated variants both for a metamodophos application at ear emergence (0.25 t per hectare) and for dimethoate to the wheat flowering (0.23 t). In 1986 we faced the necessity of spraying against cereal aphids and wheat blossom midges in order to avoid yield losses. Yields from individual plots produced for both dates of application similar yield differences between treated and untreated plots metamidophos 6 %, dimethoate 7 %). For the dimethoate application they could be substantiated statistically on the basis of the single-ear mass. REFERENCES BASEDOW Th. 1975. Neues über Biologie und Bekämpfung der Weizengallmücken. Kali-Briefe (BüntehoO, 12, 1-9. FREIER B., MATTHES P., WETZEL Th. 1982. Entscheidungshilfen zur kurzfristigen Befallsvorhersage und zur gezielten Bekämpfung der Getreideblattlaus (Macrosiphum avenae Fahr.) im Winterweizen.Nachr.-Bl. Pflanzenschutz DDR, .afi, 192-196. KÖNER H.J., WIND F., FRITZSCHE R., GEISSLER K. 1984. Erfahrungen und Ergebnisse beim Einsatz von Filitox im Hackfruchtanbau. Nachr. -Bl. Pflanzenschutz DDR, .a.8., 39-42. LÜBKE M. 1982. Untersuchungen zum Massenwechsel, zur Schadwirkung, Überwachung und Bekämpfung von Weizengallmücken. Halle-Wittenberg. Martin-Luther-Univ. Diss. A - so - WETZEL Th. 1983. Zur Durchsetzung eines integrierten Pflanzenschutzes bei der Bekämpfung wichtiger Schadinsekten des Getreides. Nachr.-Bl. Pf/,anzenschutz DDR, az,93-101. WETZEL Th., HOLZ F., STARK A. 1987. Bedeutung von Nützlingspopulationen bei der Regulation von Schädlingspopulationen im Getreidebestand. Nachr. Bl. Dt. PfianzenschutzdDDR,�1-7. WETZEL Th., SPAAR D. 1985. Zum integrierten Pflanzenschutz gegen Schadinsekten des Getreides. Wiss. Beitr. Martin-Luther-Univ. Halle Wittenberg, 61, fil, 14-23. - 51 - VARIABILITE INTERCLONALEDANS LA PRODUCTION DE FORMES SEXUEES CHEZ LE PUCERON DES CE.REALESRHOPALOSIPHUM PADI J. C. SIMON & C. A. DEDRYVER INRA, Laboratoire de Recherches de la Chaire de Zoologie de l'ENSAR, Domaine de la Motte, F 35650 LE RHEU SUMMARY The aim of this study was to analyse the response of several clones of Rhopalosiphum padi L., collected on primary and secondary hosts in Britain and France, submitted to sexual inducing conditions in order to appreciateinterclonal variability in R. padi populations. Our clones, after sexual morph induction, were caracterized depending on their own life cycle pattems. As described on Myzuspersicae Sulz., fourtypes of clonal responses have been found which correspondto holocyclic, anholocyclic, androcyclic and intermediate responses. Tue local life-cycle strategies of R. padi are discussed on the basis of the coexistence of these differents types of clones. INTRODUCTION Dans les regions a climat tempere, les aphides se reproduisent par parthenogenese cyclique et la phase sexuee annuelle, realisee generalement a l'automne, est essentiellement induite par l'augmentation de la scotophase, en conjonction, pour certaines especes, avec la baisse de la temperature (Lees, 1966; Rille Ris Lambers, 1966). Cependant, a partir de ce schema reproducteur initial, certains clones voire certaines especes de pucerons ont perdu partiellement ou totalement Ja capacite a produire des formes sexuees : les etudes portant sur des aphides comme Myzus persicae Sulz. ou Aphis gossypii Glov. et plus particulierement les travaux de Blackman (1971, 1972, 1974) et de Takada (1988) ont mis en evidence une forte variabilite intraspecifique des modes de reproduction de ces especes et des types de cycles evolutifs annuels qu'elles sont susceptibles de realiser. - 52 - Tableau 1 : Origines et dates de collecte des clones de R. padi soumis a des conditions de photophase courtes et de temperatures basses. CLONES SITES DE COLLECTE Pl.ANTES-HOTES DATES RPLARS Long Ashton (Avon, G.B.) P.padus 05/87 RPCAENl Caen (Calvados, F.) P.padus 05/87 RPRENNES Rennes (Ille & Vilaine, F.) P.padus 05/87 RP_MUR Mur-de-Bretagne(Cötes d'Armor,F.) P.padus 05/87 RPCAEN2 Caen (Calvados, F.) P.padus 06/88 RPBEAULIEU Rennes(Ille & Vilaine, F.) P.padus 05/88 RPLEGER st LegerVauban (Yonne, F.) P.padus 05/88 RPLERHEUl Le Rheu(Ille & Vilaine, F.) Bio! Olf78 RPLERHEU2 Le Rheu(Ille & Vilaine, F.) Orge 01/89 RPLERHEU3 Le Rheu(Ille & Vilaine, F.) Orge 01/89 RPLERHEU4 Le Rheu(Ille & Vilaine, F.) Orge 01/89 Tableau 2 : Nombres moyens (n=5) et ecarts-types (entre parentheses) des differents morphes composant la descendance a 15°C, 10h de photophase, des femelles apteres de 11 clones de R. padi. MORPHES EXULES EXULES %DE GYNOPARES MALES GYNOPARES CLONES APTERES AILES RPLAR S 0 0 16.2(3.4) 18.0 (5.9) 48.4(5.3) RPCAENl 0 0 17.2(5.9) 10.2 (4.0) 61.4(13.0) RPRENNES 0 0 8.6 (1.9) 21.4(7.8) 31.2(13.7) RPMUR 0 0 14.8 (3.5) 15.4 (2.9) 44.4(4.7) RPCAEN2 0 0 26.0(3.5) 12.4 (2.2) 67.6 (5.7) RPBEAULIEU 0 0 21.2 (1.6) 13.2(4.0) 62.4(9.0) RPLEGER 0 0 23.2 (2.5) 1.0(1.3) 96.2 (4.7) RPLERHEUl 32.0(7.3) 3.0(3.0) 0 1.8 (1.2) RPLERHEU2 52.6 (8.8) 1.6(2.1) 0 0 RPLERHEU3 41.6 (13.5) 0 0 0 RP LERHEU4 44.2 (10.0) 0.2 (0.4) 0 0.4(0.5) - 53 - Dans certaines regions comme l'ouest de la France (Dedryver & Gelle, 1982 ; Dedryver, 1983) et le sud de l'Angleterre (I'atchell et al, 1988 ; Hand, 1989), R. padi peut realiser concurremment un holocycle et un anholocycle. Cependant la nature precise des relations entre les populations holocycliques et anholocycliques de cette espece et les facteurs qui deterrninent quelle proportion d'individus d'une population repond aux stimuli de la production des formes sexuees sont encore meconnus. C'est pourquoi, compte-tenu de l'importance econornique de R. padi, il nous a paru opportun d'analyser la variabilite des cycles evolutifs dans les populations naturelles de cette espece d'autant qu'ils semblent jouer un röle important dans l'epiderniologie de la Jaunisse Nanisante de l'Orge (JNO), lorsqu'elle est etudiee dans une zone geographique donnee (Tatchell et al., 1988; Simon et al., 1991). Nous avons donc sournis,dans cette etude, des clones de R. padi d'origines botaniques (höte primaire et hötes secondaires) et geographiques (France, Grande Bretagne) diverses a des regimes de courte photophase et de basse temperature (Dixon & Glen, 1971), afin d'apprecier le mode de reproduction qu'ils developpent dans ces conditions experimentales et de deduire de cette reponse le type de cycle evolutif qu'ils sont susceptibles de realiser. MATERIEL ET METHODES Onze clones de R. padi dont les origines botaniques, geographiques et les dates de collecte sont mentionneesdans le tableau 1, ont ete etudies. Ces clones, dont chacun constitue une lignee issue d'un unique descendant, sont maintenus en culture depuis leur recolte dans des conditions de photoperiode et de ° temperature (l8 C, 16h de photophase) assurant la reproduction parthenogenetique continue des pucerons. Pour chaque clone etudie, cinq larves a pterotheques de quatrieme stade provenant de ° l'elevage sont exposees a un regime de 15 C, 10h de photophase dans une etuve refrigeree programmable dispensant une intensite lurnineuse d'environ 5000Lux a 50 cm de la source. Elles composent la premiere generation (GO) a etrestimulee. La descendance de ces pucerons qui se sont developpes en adultes ailes, constitue la generation-fille (Gl). Parmi celle-ci, seules cinq femelles (toutes apteres) sont suivies pour chaque clone et maintenues dans les memes conditions de photoperiode et de temperature. Tous les descendants de ces femelles apteres (G2) sont isoles quotidiennement et places individuellement sur une plantule de ble cultivee dans un tube en verre (80 x 10 mm) rempli de gelose et recouvert d'une microcage en polystyrene cristal (140 x 16 mm). Le morphe de - 54 - L16:D8 l8°C 4EME STADE LARVAIRE ------Go _____ ,::-J VA VA L10:D14 10/15°C cS � � • mn VA Vl �N GY M � a1-�) VA VI. VA OV OV Figure 1 : Modes de reproduction realises par R. padi : VA = virginipare aptere, VL = virginipare aile, IN = intermorphe, M = mäle et OV = ovipare. - 55 - chacun d'entreeux est identifie au stade adulte. Un test de choix entreune feuille de P. padus et une feuille de ble pennet de differencierles femellesailees obtenues en G2. Dans le cas des clones RP LE RHEU2,RP LE RHEU3, et RP LE RHEU4, la troisieme generation apres l'induction (G3) est egalement analysee de la meme maniere que la deuxiemegeneration (G2). Ces trois clones sont par ailleurs soumis ii. un second regime de temperature et de photoperiodede lO"C, 10h de photophase et suivis pendant deux generations (Gl et G2) selon le protocole expose ci-dessus. RESULTATS - Le nombre moyen des differents morphes composant 1a descendance en G2 de cinq femellesexposee ii.15"C, 10 h de photophase est indique pour chaque clone dans le tableau 2. Tous les clones collectes sur P. padus presentent une reponse holocyc!ique qui se caracterise par un processus de reproduction comprenant deux phases successives ; la production de gynopares puis celle de mfiles. Le pourcentage de gynopares dans la descendance peut varier considerablement selon les clones (tableau 2), de 31 % pour RP RENNES a 96 % pour RP LEGER, mais il varie egalement e�tre les individus d'un meme clone. C'est ainsi que parexemple trois des cinq parentsde RP LEGERne produisentque des gynopareset aucun mfiledans leur descendance de premieregeneration. Deux clones collectes sur graminees,RP LERHEU2 et RP LE RHEU3 presentent une reponse anholocyclique.Celle-ci presente deux caracteristiques - i) aucun des individus dont on a suivi la descendance en G2 (pour cinq parents) puis en G3 (pour trois parents) ne produit de gynopares ou de mäles, ils fonnent seulement des exules apteres (RP LE RHEU3) ou un melange d'exules apteres et de quelques ailes (RP LE RHEU2); - ii) la fecondite totale des individus de ces deux clones est significativement plus elevee que celle des parents de tous les autres clones (tableau 2) (P < 0.05, test de comparaisonde moyennes Newman-Keuls). Les deux autres clones collectes sur graminees, RP LE RHEUl et RP LE RHEU4 presentent une reponse androcyclique : ils fonnent des femelles parthenogenetiques, essentiellement des exules apteres, mais egalement quelques mfiles (beaucoup moins que les clones holocycliques) en fin de periode de reproduction. Cette reponse androcyclique n'est pas toujours exprimee par Ja totalite des individus testes pour un clone donne : ainsi chez Je - 56 - clone RP LE RHEUl, quatre femelles sur les cinq testees sont andropares et seulement deux femelles sur cinq ont donne des mfilesen G2 chez le clone RP LE RHEU4.Toutefois, pour ce dernier clone,la productionde mäles est renforcee en G3 : non seulement le nombre de mfiles formes par femelleest plus important (troismfiles par parenten moyenne en G3 contre un en 02) mais tous les individus testes forment des mäles. D'une maniere generale la productionde mfiles debute plus tardivement chez les clones androcycliquesque chez les clones holocycliques. - A 10·c, 10 h de photophase la reponse des clones RP LE RHEU2et RP LE RHEU3 est anholocyclique et celle de RP LE RHEUl androcyclique, comme a 15·c, 10 h de photophase. Par contre le clone RP LE RHEU4 presente un type de reponse original : les cinq individus de la Gl analyses forment en premier lieu en G2 de nombreux exules apteres en melange avec quelques femelles ailees, puis en second lieu des mfiles. Ces femelles ailees, soumises a un test de choix entre ble et P. padus, se revelent appartenir ll. deux categories : la premiere est constituee d'exules qui s'installent et se reproduisent uniquement sur ble apres 72 heures d'observation, la seconde est composee d'individus qui, apres le meme delai, produisent des exules apteres sur ble mais egalement des femelles ovipares sur P. padus, ces demieres etant cependant en nombre plus restreint. Cette categorie de pucerons ailes constitue une forme intermediaire, ou intermorphe, entre exule aile et gynopare. Le nombre d'intermorphes et de mfiles est faible puisqu'il represente respectivement6.5 % et 7.0 % de la descendance cumulee des cinq parents. La figure 1 resume les differents morphes susceptibles d'etre formes par R. padi en fonctiondu clone, du type d'inductionet de la generation. DISCUSSION - CONCLUSION Quatre types de reponse a des conditions de photoperiode et de temperature connues pour induire la production de gynopares et de mäles chez R. padi (Dixon & Gien, 1971) ont ete obtenues apres l'analyse de la descendance de onze clones de cette espece. Ces types de reponse sont tresproches de ceux qui ont ete precedemment decrits chez A. gossypii (Takada, 1988) et chez M. persicae (Blackman, 1971, 1972). Les reponses holocycliques que nous avons observees sont globalement semblables ll. celle detaillee par Dixon & Gien (1971), c'est ll.dire strictes : seuls des gynopares et des mfiles sont produits. Cependant, notre echantillon de clones preleves sur höte primaire est tropfaible pour qu'on puisse affinner qu'il n'existe pas, chez cette espece, de clones developpant des l 1 - 57 - reponses holocycliques partielles, telles que celles observees par Blackman (1971) chez M. persicae et par Hand & Wratten (1985) ainsi que Wegorek & Dedryver (1987) chez Sitobion avenaeF.. La reponse anholocyclique exprimee par deux clones (RP LE RHEU2 et RP LE RHEU3), collectes sur cereales en hiver ne semble pas varier en fonction des conditions d'induction puisqu'elle est stable selon la temperature et le nombre de generations, tout au moins dans les lirnitesde notreetude. Nous confirmons ainsi qu'il parait exister, dans l'ouest de la France, des clones de R. padi ayant perdu toutes capacites a formerdes sexues (Dedryver & Gelle, 1982). Par ailleurs, la fecondite totale des clones anholocycliques de R. padi est, dans des conditions inductrices de la phase sexuee, tres superieure a celle des clones holocycliqueset androcycliques. De tels resultats ont egalement ete obtenus par Newton & Dixon (1988) sur S. avenae. Deux autres clones (RP LE RHEUl et RP LE RHEU4), collectes egalement sur cereales en hiver, ont developpe une reponse androcyclique. Comme chez M. persicae (Blackman, 1971), les clones androcycliques de R. padi testes se caracterisent par une production de mfiles plus faible que celle des clones holocycliques, certains individus de ce type de clone pouvant ne pas exprimerleur capacite a formerce morphe. Cette caracteristique donne a penser qu'en plus de la perte de l'aptitude a produire des gynopares, ces clones voient affecter leur mecanisme de production des mfiles (induction maternelle, determinisme chromosornique du sexe). Le clone RP LE RHEU4presente, apres une stimulation a lO"C, 10 h de photophase, une reponse particuliere caracterisee par la production de males et d'une formeintermediaire entregynopare et exule aile. Cet intermorphede R. padi a ete trouve sur le terrain et decritpar Tatchell & Parker (1990) en Grande Bretagne. Sa nature est differente de celle des morphes intermediaires obtenus experimentalement pour des conditions d'induction-seuil (Crema, 1971 ). Seule l'etude de son componement pourrait nous renseigner sur ces capacites reelles a se reproduire sur graminees puis a regagner un böte primaire pour y donner naissance a des ovipares. Si l'on s'interesse plus particulierement aux clones recoltes dans les environs du Rheu (3 holocycliques, 2 anholocycliques et 2 androcycliques), on voit que les populations de R. padi y sont susceptibles d'etre composees a cenaines periodes de l'annee d'un melange de clones pouvant realiser des cycles evolutifs differents. - 58 - Les bases de la coexistence entre ces diverses categories clonales paraissent essentiellement fonction du climat hivemal, qui permet ou non la survie des fractions parthenogenetiques, et de la frequence de l'höte primaire dont la rarete en Bretagne limite probablement l'importance de la fractionholocyclique localeau printemps. Deux hypotheses non exclusives pennettent d'expliquer le maintien local a long tenne des populations composees des differents types de clones : d'une part leur renforcement periodiquepar des apports d'individus ailes exogenes, d'autrepart la possibilite qu'auraient les mäles issus de clones androcycliques de participer a la reproduction sexuee ce qui constituerait une sauvegarde de populations a potentialites anholocycliques (Blackman, 1972). BIBLIOGRAPHIE BLACKMAN, R. L., 1971. Variation in the photoperiodic response within natural populations of Myzuspersicae Sulz.. Bull. Ent. Res. 60 : 533-546. BLACKMAN, R. L., 1972. Tue inheritance of life-cycle differencesin Myzus persicae (Sulz.) (Hem., Aphididae). Bull. Ent. Res. 62: 281-294. BLACKMAN, R. L., 1974. Life-cycle variation of Myzus persicae (Sulz.) (Horn., Aphididae) in different parts of the world, in relation to genotype and·environment. Bull. Ent. Res. 63 : 595-607. CREMA, R., 1971. Changes in the ovary of Acyrthosiphon pisum Harris during transition from amphigony to parthenogenesis. Monitore Zool.Ital. 5: 81-90. DEDRYVER, C. A., 1983. Evolution des populations de Rhopalosiphum padi L. sur son höte primaire, Prunus padus L. dans deux stations du nord et de l'ouest de la France. Agronomie 3 : 1-8. DEDRYVER, C. A. & A. GELLE, 1982. Biologie des pucerons des cereales dans l'ouest de la France. IV - Etude de l'hivernationde populations anholocycliquesde Rhopalosiphum padi L., Metopolophium dirhodum Wlk. et Sitobion avenae F. sur repousses de cereales, dans trois stations de Bretagne et du Bassin Parisien.Acta Oecologica. Oecol. Applic. 3 : 321-342. DIXON, A. F. G. & D. M. GLEN, 1971. Morph determination in the bird cherry-oat aphid, Rhopalosiphum padi L. Ann. appl. Biol. 68 : 11-21. HAND, S. C., 1989. The overwintering of cereal aphids on Gramineae in southem England, 1977-1980. Ann. appl. Bio!. 115: 17-29. HAND, S. C. & S. D. WRATTEN, 1985. Production of sexual morphs by the monoecious cereal aphid Sitobion avenae. Entomol. exp. appl. 38: 239-247. - 59 - Hil,LERIS LAMBERS, D., 1966. Polymorphism in Aphididae. Ann. Rev. Ent. 11 : 47-78. LEES, A. D., 1966. Tuecontrol of polymorphism in Aphids. Adv. Ins. Physiol. 3 : 207-277. NEWTON, C. & A. F. G. DIXON, 1988. A preliminary study of variation and inheritance of life-history traits and the occurence of hybrid vigour in Silibion avenae (F.) (Hemiptera : Aphididae). Bull. ent. Res. 78 : 75-83. SIMON, J. C., C. A. DEDRYVER, J. S. PIERRE, 1991. ldentifying bird cherry-oat aphid Rlwpa/osiphumpadi emigrants, alate axules and gynoparae : application of multivariate methods to morphometricand anatomical features. Entomol. exp. appl. (a paraitre). TAKADA, H., 1988. Interclonal variation in the photoperiodic response for sexual morph production of Japanese Aphis gossypii Glover (Horn., Aphididae). J. appl. Ent. 106 : 188-197. TATCHELL, G. M., R. T. PLUMB & N. CARTER, 1988. Migration of alate morphs of the bird cherry aphid (Rlwpa/osiphum padi) and implications for the epidemiology of barley yellow dwarfvirus. Ann. appl. Biol. 112 : 1-11. TATCHELL, G. M. & S. J. PARKER, 1990. Host plant selection by migrant Rlwpalosiphum padi in autumn and the occurence of an intermediate morph. Entomol. exp. appl. 54 : 237-244. WEGOREK, P. & C. A. DEDRYVER, 1987. Action de la temperature et de la photoperiode sur la production de formes sexuees par differents clones du puceron des cereales Sitobion avenae. Entomol. exp. appl. 45 : 89-97. - 60 - Reasons for and consequences of the serious BYDV infestation in Northern Germany 1989 C. Borgemeister1 and H.-M. Poehling2 1 Institut für Pflanzenkrankheiten und Pflanzenschutz der Universität Hannover, Herrenhäuser Str. 2, D-3000 Hannover 21, FRG 2 Institut für Pflanzenpathologie und Pflanzenschutz der Universität Göttingen, Grisebachstr. 6, D-3400 Göttingen, FRG Summary In 1988/89 the first heavy BYDV outbreak in the FRG was recorded. Damages occured mainly in winter wheat. Figu res of a reduction of wheat yields up to 40% were recorded. The epidemic was mainly caused by an early spring immigration of Sitobion avenae, the predcminant aphid vector in Northern Germany. The heavy yield las ses were probably not only due to the virus disease but also to dry wheather conditions in May and June 1989. The necessesity of a specific forecast system for 'the regional circumstances in Northern Germany is discus sed. 1.1 Introduction In the past the barley yellow dwarf virus (BYDV) has never been of great concern for the production of cereals in the Federal Republic of Germany. Al'l:hough cereal aphids, the vector of the disease, are the most important economic pest, esp�cially in winter wheat (BASEDOW 1976), the pro portion of virus infected plants rarely exceeded a rate of 1% (HUTH 1990). The last heavy outbreak of BYDV occured 1977 in some regions of Schleswig-Holstein (JUNGA 1989). The major BYDV infection :i.n Northern Germany 1988/89 has now initialized an intensive discussion in the FRG whether this disease could become a permanent problem in the future. Unfortunately the 1988/69 epidemic was not accompa nied by &ny scientific investigations so in this paper we can only describe the present situation in Northern Germany. 1.2 General outlook The main reason for last years heavy aphid- and BYDV out break was probably the mild autumn in 1988, which enabled an unusual long lasting aphid flight and the extraordinary warm winter and spring in 1988/89 (figure 1). Because of - 61 - the high temperatures during the winter months a great part of the anholocyclic aphid clones survived this period. Although anholocycly, especially in the case of Sitobion avenae (F.) (Homoptera: Aphididae), the most important aphid species in Northern Germany, can even be found in the very north of Germany (HöLLER 1990) these clones usually show a high degree of mortality caused by the normal frost periods. Additionally the outreageous warm period in �arch 1989 allowed an extraordinary early hatching of holocyclic S. avenae clones and a fast establishment of the aphids in winter cereals. Taking into account the time when the first distinct symptoms were visible in the fields, i.e. the late April and the beginning of May 1989, it is obvious that the main infection in the case of winter wheat was set during the early spring 1989. The 1988 autumn infection of winter barley produced only minor damages. BYDV infected barley reacts very sensible to minus degrees (HUTH 1990) and in this sense the mild winter 1988/89 tempered the threat of the disease. The spring aphids, in their majority s. avenae, partly originating from wild grasses and pasture, were therefore probably the predominant virus vectors. HUTH ( 1990) could detect PAV-, MAV-, and RPV-strains of BYDV in several comrnon wild gras species in the FRG, like Lolium perenne, Bromus saecalinus, Bromus sterilis, Dacty li s gl omerata and Agropyron repens and regards them beside maize as the most important sources of the virus. Figure 2 shows the population trends of cereal aphids in three differ&ld: locations in the region of Göttingen/Lower Saxony. Compared wi th other years the aphid deve 1 opment shifted at least four to six weeks in advance (POEHLING ) . Ernpirically the current West German threshold of 20% aphid infested wheat stems (BASEDOW et al. 1983) is reached in the northern part of Gerrnany during the second half of June. Dry wheather conditions at the end of June 1989 which caused a premature ripening of the wheat and high densities of aphid specific predators, in their majority Coccinellids, produced an early break-down of the aphid population. The average wheat yields in 1989 were drastically reduced. In certain regions figures of a reduction up to 40% of yields were reported (BARTELS & �INTGEN 1990). The dang�r of an early BYDV infection in April and May 1989 was neither recognized by the advisory boards nor by the farmers. Taking into consideration the few cases of BYDV in former years in Germany simply nCJ--11e expected the wheat yields to be influenced in such a manner. Consequently the aphids were mainly regarded as a direct damaging pest than as a virus vector. In this sense not all insecticide treatments, especially the late ones, obtained sufficient results. Concerning last years experiences late appl ications in this context were even those which were FIGUR& 1 Meteorological Values: September 1988 - August 1989 O mm raint all c 200 20 dataa, Hannover Airport (monthly average valueal � 150 15 '\��""' 100 �- -, 10 c,,� 50 5 0 1 1 l:???1 1 'O SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG 1988 1989 � rainfall D rainfall --*-"temperatures -B- temperatures (09.88·08.89) (average valuea•l (09.88·08.89) (average valuea•) • • dataa lrom 1961·1980 source: Wetteramt Hannover - 63 - lead through around ear emergence (EC 55). In regular years an insecticide treatment at this stage is rather regarded as a prophylactic procedure. Figure 3 shows the effects of different timed Fenvalerate appl ications on yield and the frequency of observed BYDV related symptoms (expressed by the not unequivocal term "black ears"). Concerning the levels of aphid infestation the two insecticide plots can not be directly compared because the datas only reflect the situation on the 19th of June 1989, three days after the late Fenvalerate spraying. The early treated plots had higher yield values and showed fewer BYDV related symptoms. This corresponds with observations from regions with routine Deltamethrin applications in EC 49 against saddle gall midges (BARTELS & WINTGEM 1990). In contrast to these results there are reports of multiple treatments with Demeton-s-methyl that had little effect on the yield level (HUTH 1990). In general no insecticide application can absolutely prevent a primary BYDV infection, especially if the vector population like in 1988/89 immigrates over longer period into the fields. Without denying the obvious BYDV infection in 1988/89 it is not possible to quantify exactly the damage caused by the virus alone. What made the situation in 1988/89 so severe was more an interplay of several components. In this connection the extreme drought in May and .June 1989 cer tainly plays a central role. lt is well known from the epi demiology of fungus diseases that a second stress factor 1 ike water stress can aggravate the damages for the host plant (OERKE & SCHöNBECK 1986). Additionally the heavy aphid pressure alone was good enough for a severe reduction of the cereal yields. Beside the red flag leafs the most commonly observed symp tom which were brought into connection with the virus were, as mentioned before, the darkish discoloured wheat ears. The main cause for that were secondary infections with saprophytic sooty noulds. On the other hand these fungi not only settle on virus infected plant but also on honeydew excretions as a consequence of heavy aphid infestation (RABBINGE & MANTEL 1981). An ELISA screening of 56 wheat ears exhibiting these symptoms revealed that at least 27% were free of any virus or the virus content was below the limits of the testing method (HUTH 1990). Summarizing all these observations it is unlikely that all yield deficits were solely caused by the BYDV infection. Therefore it seems admissible to postulate that the extraordinary drought in May and .June 1989 worsened the situation to a large extent and that it is not possible at the present to relate the observed damage to certain factors. It also seems to be precipitate to draw general conclu sions, 1.e. prophylactic insecticiede treatments or the ad Aphid densities 1989 FIGURE 2 (three locations in Lower Saxony - FRG) % aphid infested stems �� 100r--���� 80 60 "" 40 20 Ql&ffll �II! �II 1 �II 15.5 20.5 25.5 30.5 4.6 9.6 14.6 19.6 24.6 29.6 4.7 � Einum • • peak aphid density � Harste 0 Hilprechtshausen source: BARTELS & WINTGEN 1990 FIGURE 3 Effects of two Fenvalerate treatments on the population density of cereal aphids, yield and "black ears" Einum (FRG) 1989 % aphid infested stems yield (dt/ha) 100 ,------· ------� 100 � % aphid infested stems 19.06.89 D "black ears· 80 M yield (dt/ha) 80 60 60 �al 40 f- tiiJ@;] � � �� � 1 40 201- � � ==1 � � � 120 l__y%'8=' 0 untreated control Fenvalerate (0,3 1/ha} Fenvalerate (0,3 1/ha} 0 application: 16.06.89 (EC 55}application: 31.05.89 (EC 49} source: BARTELS & WINTG EN 1990 - 66 - hoc establishment of distinct thresholds, from the experiences of only one year with a major infection. An intensification of the research on BYDV for the specific situation in Northern Germany with the aim to elaborate an economic threshold for these circumstances should be the right answer. Scientific data of the BYDV epidemiology and the overwintering strategies of the vector population for Germany are very scarce. Therefore it is the duty of scien tific research to fill these gaps so that substantial advi ces can be given to the farmers as soon as possible. In the meantime only intensive monitoring of the aphid development plus routine ELISA testings in the threatened regions may hel� to contain the prophylactic use of insecticides with all their detremental consequences for the whole ecosystem. REFERENCES 1. Bartels, M. and Wintgen A. (1990): Gerstengelbver zwergungsvirus - Eine neue Gefahr für den Weizen. PSP (in press) 2. Basedow, T. (1976): tiber das Auftreten der Getreide blattlausarten (Horn., Aphididae) in norddeutschen Wei zenanbaugebieten (1974/75). Anz. Schädlingskde., Pflan zenschutz, Umweltschutz. 49, 9-14 3. Basedow, T., Bauers, C. and Lauenstein, G. (1983): Zur Bekämpfungsschwelle der Getreideblattläuse an Winter weizen (vorläufige Kitteilung). Nachrichtenbl. Deut. Pflanzenschutzd. 35, 141-142 4. Höller, c. (1990): Overwintering and hymenopterous parasitism in autumn of the careal aphid Sitobion avenae (F.) in northern FR Germany. J. Appl. Ent. �109, 21-28 5. Huth, W. (1990): Barley yellow dwarf - ein permanentes Problem in der Bundesrepublik Deutschland? Nachrichtbl. Deut. Pflanzenschutzd. 42 (1), 33-39 6. Junga, u. (1989): Gelbverzwergungsvirus der Gerste in 'Winterweizen. Bauernblatt/Landpost_!!, 28-32 7. Oerke, E.-c. and Schönbeck, F. (1986): Zum Einfluß abiotischer Str�ßfaktoren auf das Wachstum von Gerste und Bohne und deren Prädisposition gegenüber Schaderre gern. z. Pfl.Krankh. u. Pfl.Schutz 93 (�), 561-573 8. Poehling, H.-M. (1S88): Influence of cereal aphid control on aphid specific predators in winter wheat (Homoptera: Aphididae). Entornol. Gener. 13 (3/4), 163- 174 9. Rabbinge, R. and Mantel, P. (1981): Monitoring for cereal aphids in winter wheat. Neth. J. Pl. Path. 87, 25-29 - 67 - DYNAMIQUE DES VECTEURSET DES vm.usDE LA JAUNISSENANISANTE DE L'ORGE DANSLE BASSINDE RENNESA L'AUTOMNE 1989 Francoise LECLERCQ-LE QUILLEC & C.A. DEDRYVER INRA, Laboratoire de Recherches de la Chaire de Zoologie de l'ENSAR, Domaine de la Motte, F 35650 LE RHEU SUMMARY Cereal aphids were caught alive by a special suction trap in Le Rheu during the autumn 1989 and allowed to transmit BYDV on test plants (oat, cv Blenda). BYDV strains were identified by ELISA procedure using monoclonal antibodies. Only Rlwpalosiphum padi L. alates were caught from September to November ; 35.4 % were infectious and transmitted PAV and RPV alone or in mixture, and MAV in mixedinfections with other strains. The percentages of each strain in the pooled transmissiontests were rather similar to the percentages of each strain in an infected barley sample collected in an adjacentfield at the same period. Les regions de l'Ouest de la France sont particulierement sujettes aux epidemies de Jaunisse nanisante de l'orge (J.N.O. ou B.Y.D.), du fait de leurs caracteristiques ecoclimatiques. Les automnes et hivers generalement doux y permettent une multiplication importante des pucerons vecteurs sur certains reservoirs, en particulier le mai"s (HENRY & DEDRYVER, 1989), puis le maintien, voire le developpement, de populations aphidiennes anholocycliques sur l'orge et le ble au cours de l'hiver (LECLERCQ-LE QUILLEC & DEDRYVER, 1990). De ce fait les infections primaires des jeunes cereales sont souvent massives et la dissemination secondaire des virus importante. Plus generalement, la succession annuelle de differentes cultures de graminees multiplicatrices de virus et de pucerons (cereales a pailles-mai"s) ainsi que l'abondance de reservoirs permanents et perennes comme les graminees - 68 - fourrageres (HENRY & DEDRYVER, 1991), n'y permettent generalement pas de rupture de l'association virus-vecteurs-plantes au cours de l'annee. Dans ces regions, la prevision des risques encourus a l'automne par les jeunes semis de cereales peut etre faite sur la base des captures de pucerons des cereales au piege a succion de 12.2 m de haut (type Rothamsted) du reseau AGRAPHID (ROBERT & CHOPPIN DE JANVRY, 1977 ; HULLE & GAMON, 1989). Il existe en effet une relation particulierement stable entre les captures hebdomadaires du principal vecteur, Rhopalosiphum padi L. et les taux d'infestation de plants d'orge "pieges" disposes au champ et renouveles chaque semaine (GILLET et al., 1990). Cette relation pennet des a present de simuler, avec un pas de temps d'une semaine, les risques d'infestation des cultures par les pucerons. Cependant la prevision des risques d'infection virale correspondants necessite une ponderation des resultats precedents par le pouvoir virulifere des pucerons. Celui-ci est jusqu'ici estime indirectement, par detection en ELISA des virus de la J.N.O. dans les plants d'orge "pieges" precedemment mentionnes (PIERRE et al., 1987). Afin de simplifier les methodes experimentales et de raccourcir les delais d'estimation des risques, on peut envisager de tester le caractere virulifere de pucerons captures vivants (ce qui est impossible avec le piege de 12.2 m) a l'aide d'un piege specialement adapte. Ceci peut se faire directement, en detectant en ELISA la presence de virus dans les pucerons captures (TORRANCE, 1987) ; ou indirectement par l'intermediaire de plantes-tests (PLUMB, 1976 ; A'BROOK & DEWAR, 1980). La premiere methode etant encore en voie de mise au point, nous exposons dans cet article une application de la seconde. La dynamique des pucerons pieges et des isolats qu'ils ont transmis y est comparee a celle des pucerons et des virus dans un champ d'orge au cours de la meme periode (automne 1989). MATERIELS & METHODES Au cours de l'automne 1989 les pucerons ailes en deplacement aerien sont captures joumellement a l'aide d'un piege a succion specialement adapte a la recolte des insectes vivants, d'un modele analogue a celui fonctionnant au Rothamsted Insect Survey a Harpenden (PLUMB, 1976). Ce piege mesure 1,5 m de haut. Il est muni d'un ventilateur helico1de de 450 mm de diametre debitant 3 environ 3000 m d'air a l'heure. Le piege est place dans le parc meteorologique de l'INRA au Rheu, a proximite du piege a succion de 12,2 m du reseau AGRAPHID, - 69 - dans une zone de grandes cultures. Pour des raisons liees a la survie des pucerons captures, le piege ne fonctionne que 5 jours par semaine, de 9 h a 16 h. Les especes d'aphides piegees dans la joumee sont identifiees puis les pucerons infeodes aux cereales sont installes individuellement sur des plantules d'avoine (cv. Blenda) qui sont ensuite entreposees a 18'C, 16 h de photophase pendant 5 jours afin d'assurer une eventuelle transmission virale. Ces plantules sont ensuite traitees a la deltamethrine (Decis a 0.5 ml/1)puis placees en serre a l'abri des contaminations de pucerons pendant 15 jours. Les plantules sont finalement testees en ELISA comme ci-dessous. Une parcelle d'orge d'hiver (cv. Express) situee a quelques centaines de metres du piege, semee le 13 septembre 1989, fait l'objet d'un echantillonnage bi hebdomadaire de fin septembre a fin decembre. A chaque date d'echantillonnage 360 plants d'orge sont preleves dans la parcelle, par groupe de 30 plantes consecutives. Les pucerons qui s'y trouvent sont determines au champ d'apres des criteres d'observation macroscopiques et les plantules sont ensuite testees individuellement en ELISA en vue de la detection des diffärents virus presents. Pour les 2 experimentations, la detection des virus transmis est realisee en ELISA indirect a 2 sites, utilisant comme capteurs des serums polyclonaux : PcB de Bioreba (Bäle, Suisse); Pc PAV, Pc MAV et Pc RPV fournis par H. LAPIERRE (INRA, laboratoire de virologie, CNRA Versailles). Trois anticorps monoclonaux, MAC 91, MAC 92 et MAFF2 du MAFF (Ministry of Agriculture Fisheries and Food, Harpenden, Grande Bretagne) sont employes, comme revelateurs des virus PAV, RPV et MAV (ROCHOW, 1970). RESULTATS R. padi est la seule espece de pucerons des cereales capturee par le piege de 1,5 m entre septembre et novembre 1989. Dans le meme temps cette espece constituait 97,2 % des captures de pucerons des cereales au piege de 12,2 m, contre 2,2 % pour Sitobion avenae F. et 0,3 % pour Metopolophium dirhodum Wlk. La figure 1 indique que c'est en septembre que le pourcentage de R. padi ayant transmis des isolats viraux est le plus important (62,5 %). 11 n'est plus que de 25 % en octobre. En novembre aucun R. padi virulifere n'est capture. Parmi les 23 R. padi viruliferes captures, 13 (56,5 %) ont uniquement transmis des isolats de type PAV, 2 (8,7 %) ont transmis uniquement des isolats de type RPV et aucun ne transmet d'isolat MAV pur. Cependant 8 pucerons ont transmis des isolats MAV en association avec une ou plusieurs autres souches virales: 4 avec RPV, 2 avec PAV et 2 avec PAV et RPV. - 70 - 25 20 15 Nombre 10 5 36 37 41 42 43 44 45 46 47 SEPTEMllRE OCTOBRE NOVEMBU.E Figure 1 : Nombre de R. padi tJII) et nombre de R. padi viruliferes ( �) captures a 1,5 mau cours de l'automne 1989 ßO Rhopalosiphum pad1 .40 Sitobion avenae 30 Metopolophium Pourcentage dirhodum de plantes infest6es 20 10 fi ocl 89 18 ocl 89 !ll O\ll 89 111 no• 89 „2 d�c 89 Figure 2: Infestation de la parcelle d'orge par les differentes espec�s de pucerons des cereales au cours de l'automne 1989. - 71 - La colonisation de la parcelle d'orge est representee Figure 2. L'espece R. padi colonise jusqu'a 28 % des plantes le 18/10 puis le pourcentage de plantes colonisees regresse pour se stabiliser autour de 10 % entre fin octobre et debut decembre. S. avenae et M. dirlwdum colonisent chacun moins de 2 % des plantes au cours de cette periode. Les frequences respectives de chaque souche ou virus dans les deux types d'echantillons recoltes sont assez comparables (Figure 3) : la souche PAV constitue 52 % des isolats transmis par les pucerons pieges de septembre a novembre, et 56 % de ceux detectes au champ d'octobre a decembre. La correspondance est moins bonne pour les deux autres souches : la part de RPV est moins importante dans les isolats detectes au champ (12 %) qu'elle ne l'est dans ceux transmis par les pucerons pieges (24 %). C'est l'inverse pour la souche MAV. DISCUSSION & CONCLUSION Les quantites de pucerons capturees chaque semaine par le piege a succion de 1,5 m representent entre 10 et 25 % des captures correspondantes au piege de 12,2 m, ce qui est en accord avec les resultats de PLUMB (1976) et plus recemment de SIMON (1991). L'allure generale des courbes de vol est la meme dans les deux cas ce qui indique qu'il ne semble pas y avoir de biais entre les deux types d'echantillonnages pour les captures de R. padi, tous morphes confondus. Le rapport entre !es quantites de pucerons capturees par les deux pieges explique egalement pourquoi aucun S. avenae ou M. dirhodum n'a ete piege a 1,5 m. Plus generalement cette dominance de R. padi sur les autres especes infeodees aux graminees n'est pas etonnante ; cette espece, abondamment multipliee de septembre a novembre par le mars et les graminees fourrageres, constitue plus de 90 % des captures de pucerons des cereales au cours de la meme periode au piege de 12,2 m du Rheu, de 1983 a 1987 (GILLET et al., 1990). Le pourcentage de pucerons viruliferes captures au piege de 1,5 1 m est globalement eleve (35 %) sur toute la periode de capture, mais particulierement en septembre. Ceci est beaucoup plus fort que ce qui est enregistre en Grande Bretagne, ou sur 13 annees les pucerons viruliferes n'ont jamais depasse 11,5 % du total mensuel piege (PLUMB et al., 1986) dans le cas de la J.N.O. Par contre, nos resultats sont coherents avec l'estimation par l'intermediaire de plantes pieges disposes sur le terrain, du pouvoir virulifere moyen (de 29 a 56 % selon les semaines) des R. padi a. l'automne 1989 (LADEVEZE, com. pers.) au Rheu. Ceci - 72 - 51,60" 56,30" n = 33 n = 970 • PAV O MAV !B RPV Figure 3 : Pourcentages relatifs des isolats viraux t:ransmispar les pucerons pieges (A) et detectes dans la parcelle d'orge (B) en automne 1989 (n : nombre d'ecbantillons). - 73 - confirme la gravite des risques potentiels dus a la J.N.O. dans cette region. Le fait que nous n'ayons pas trouve de pucerons viruliferes en novembre peut tenir a la taille de l'echantillon recolte (9). Cependant PLUMB (1976) n'en signale pas non plus dans le Sud de l'Angleterre, ce qui est egalement le cas certaines annees au pays de Galles (A'BROOK & DEWAR, 1980). Ceci peut etre du a une action des basses temperatures sur l'acquisition des virus par les pucerons, mais egalement au fait que les plantes d'origine des pucerons captures a cette epoque n'etaient pas ou peu contaminees. Parmi les isolats transmis par les pucerons captures, PAV est predominant, ce qui parait refleter la situation globale dans les reservoirs automnaux de R. padi : Mai:s(HENRY & DEDRYVER, 1989 ; END, com. pers.) et graminees fourrageres (HENRY & DEDRYVER, 1991). Cependant l'importance de RPV, qu'on ne detecte pas dans le mars (HENRY & DEDRYVER, 1989 ; END, com. pers.) dans nos echantillons, peut tenir aux conditions particulieres de l'ete 1989. Le mai:s ayant ete recolte debut septembre 1989 dans la region d'etude du fait de la secheresse, la principale source de pucerons a l'automne devait etre cette annee-la les graminees fourrageres, essentiellement les ray-grass, uniquement contamines par PAV et RPV (HENRY & DEDRYVER, 1991). Nous mettons d'autre part en evidence la possibilite pour R. padi de transmettre en conditions naturelles Ia souche MA V en melange avec d'autres souches, probablement par transencapsidation, tel que cela a ete montre au laboratoire par ROCHOW (1977). Enfin la bonne relation observee entre les frequences respectives des differentes souches au champ et transmises par les pucerons captures, confirme l'interet de ce type d'experimentation pour l'amelioration des methodes de prevision des risques dus a la J.N.O. BIBLIOGRAPHIE A'BROOK J., DEWAR A.M., 1980. Barley yellow dwarf infectivity of alate aphid vectors in west Wales. Ann. appl. Biol. �. 51-58. GILLET H., DEDRYVER C.A., ROBERT Y., GAMON Agnes, PIERRE J.S., 1990. Assessing the risk of primary infection of cereals by barley yellow dwarf virus in autumn in the Rennes basin of France. Ann. appl. Biol. lll, 237- 251. - 74 - HENRY Monique, DEDRYVER C.A., 1989. Fluctuations in cereal aphid populations on maize (Zea mays) in westem France in relation to the epidemiology of barley yellow dwarf virus (BYDV). J. Appl. Ent. lQl, 401- 410. HENRY Monique, DEDRYVER C.A., 1991. Occurence of barley yellow dwarf virus in pastures ofwest.emFrance. Plant patlwlogyiQ, Sous presse. HULLE M., GAMON Agnes, 1989. Relations entre les captures de pieges a succion du reseau AGRAPlilD. In "Euraphid netwok : trapping and aphid prognosis". Proceedings of an EC Experts' meeting Catane 7-9 novembre 1988, CavalloroEd. p. 153-164. LECLERCQ-LE QUILLEC Fran�oise, _DEDRYVER C.A., 1990. Dissemination des virusde la J.N.O. en parcelles d'orge d'hiver, en relation avec l'evolution des populations de pucerons vect.eurs. Effet d'un aphicide applique en trait.ement de semences. ANPP, 2e Confärence Int.emationale sur les ravageurs en agriculture, Versailles, 4-6 decembre 1990. p. 757-764. PIERRE J.S., DEDRYVER C.A., BAYON F., FOUGEROUXA., GAMON Agnes, GILLET H., de la MESSELIERE C., TAUPIN P., 1987. Previsions statistiques des pullulations de Sitobion avenae et de la vection du virus de la jaunisse nanisante de I'orge par Rhopalosiphum padi. C.R. Acad. Agric. Fr., ll(7), 153-167. PLUMB R.T., 1976. Barley yellow dwarfvirus in aphids caught in succion traps, 1969-73. Ann. appl. Biol. .B.a,53-59. PLUMB R.T., LENNON E.A., GUTTERIDGE R.A., 1986 . .Forecasting barley yellow dwarf virus by monitoring vector populations and infectivity. In : ''Plant virus epidemics monitoring, modelling and predicting outbreaks". Eds : McLEAN G.D., GARRET R.G. & RUESINK W.G., Academic Press, Sydney p. 387-398. ROBERT Y., CHOPIN DE JANVRY E., 1977. Sur l'interet d'implant.er en France un reseau de piegeage pour ameliorer la lutte contre les pucerons. Bull. Techn. Inform. Min. Agr.,�. 559-568. ROCHOW W.F., 1970. Barley yellow dwarf virus. CMI/AAB Description of plant viruses, �. 4 p. ROCHOW W.F., 1977. Dependant transmission from mixed infections. In "Aphids as virus vectors". -HARRIS K & MARAMOROSCH K Eds. AcademicPress N.Y. p. 253-273. SIMON J.C., 1991. Etude de la variabilite du cycle evolutifet recherche de son determinisme chez le puceron des cereales Rlwpalosiphum padi L. (Homopt.era: Aphididae). These Doc. Universite Paris6. 94 pp. TORRANCE L., 1987. Use of enzyme amplification in an ELISA to increase sensitivity ofdetection ofBarley yellow dwarfvirus in oats and in individual vectors aphids. J. Viral. Meth. ll, 131-138. - 75 - ADVANCES IN THE KNOWLEDGE OF BYDV EPIDEMIOLOGY IN SPAIN J. COMAS, X. PONS & R. ALBAJES Centre d'Investigaci6 i Desenvolupament Agrari de Lleida Area de Protecci6 de Conreus Av. Alcalde Rovira Roure, 177. 25006 Lleida SUMMARY Ocurrence of BYDV in the main regions growing cereal in Spain is exposed. In Northeast Spain the infectivity of winged aphid vectors colonizing winter cereal and maize has been investigated. A significant rate of alates tested were infective. Up to now testing results against PAV, RPV and MAV monoclonal antibodies seem to show that PAV is the prodominant isolate. �-1 .- Update results on cereal aphid dynamics in Northeast of Since 1983 we have been working on cereal aphid dynamics in the Northeast of Spain. The main features pointed out on the preceding meetings of IOBC (Pons & Albajes 1987a, 1987b; Comas et a7. 1989) are the following: - Aphid population is maintained troughout the season on winter cereal, maize and forage cereal as a result of aphid host crops overlapping. In our area due to the fact that most crops are under irrigation, forage cereal is sown quite early (September) and consequently there is aslo a good overlapping between maize and forage cereal. - Rhopa1osiphumpadi, Sitobion avenae, and Metopo1ophium dirhodum are the most important species. - Winter cereal crops emerging before the beginning of mid December are colonized by aphids in autumn. At that moment R.padi is the most frequent species. - Cereal aphids have an anholocyclic behaviour in our area. Aphids overwinter on cereals (aphid survival depends on the hardiness of the winter). - In spring the predominant species on winter cereal is S.avenae. S.avenae is also the most important species arriving at maize. - In our area cereal aphids mainly oversummer on maize. At the beginning of autumn the predominant species on maize is R.padi. Population levels of S.avenae are much lower. - 76 - Figyre 1.- BYDV strains identificated by different authors in the main spanish regions where cereal is cultivated. REGIONS SOURCE CM Castilla-La Mancha (1): Lister et al, 1990 CL Castilla-Leon (2): Jorda et al., 1990 AN Andalucia (3): Moriones et al.,1990 A Aragon (4): Osca, 1990 C Catalonia (5): Own data G Galicia N Navarra V Valencia - 77 - - At that moment colonization by aphids on forage cereal (usually associated with vetch) is important. 2.- BYDV research in Spain. Table 1 shows in the main Spanish regions where winter cereal is cultivated, the surfaces devoted to crops which can act as cereal aphid hosts. In Table 2 the percentages of each host related to total cereal aphid hosts surface is indicated. 3 Table 1 .- Surfaces (x10 ha) devoted to crops that can act as cereal aphid hosts in the main regions of Spain where winter cereal is cultivated. winter forage forage Region cereal �erea] maize maize rice Castilla-La Mancha 2335 29.0 5.5 6.0 0 Castilla-Leon 1383 41 .5 30.0 3.5 0 Andalucia 998 67.0 56.0 9.0 26 Aragon 854 11. 5 4.5 4.0 2 Catalonia 315 26.0 34.5 11.5 18 Galicia 89 42.5 147.0 44.0 0 Navarra 188 4.3 16.0 0.5 0 Valencia 27 1 . 5 6.0 0.5 16 SPAIN 6931 431 .0 418.0 104.0 68 Tab]e 2.- Percentage of cereal aphid hosts related to total surface devoted to crop that can act as cereal aphid hosts. winter forage forage cereal cereal maize maize rice Castilla-La Mancha 98.2 1 .3 0.3 0.2 o.o Castilla-Leon 94.8 3.0 2.0 0.2 o.o Andalucia 87.0 5.0 5.0 0.4 0.2 Aragon 93.2 1 .2 5.0 0.4 0.2 Catalonia 77.5 6.5 8.5 3.0 4.5 Galicia 27.5 13.0 45.6 13.8 0.0 Navarra 90.1 2.0 7.7 0.2 o.o Valencia 53.0 3.0 11 . 7 1 . 0 31.3 Figure 1 indicates the BYDV strains identificated in Spain by diferent authors. - 78 - 3.-BYDV presence in Northeast Spain. Since autumn 1987 we have been looking for the presence of BYDV in our area. At the beginning we tested samples against Bioreba B poljclonal, and later against PAV, RPV and MAV monoclonal antibodies supplied by the Harpenden Laboratory, MAFF (UK). - Presence of BYDV on aphid hosts. Winter cereal fields. In the spring of 1988 the percentage of cereal fields infected was very high (85%), whi le in the spring of the following year was much lower (10%). fields tested % infected spring 1988 50 85 spring 1989 35 10 Forage cerea] fie]ds. Resul ts from the winters of 1988 and 1989 show that the percentage of infected fields is always very high. In cereal vol untee rs the p resence of BYDV i noccul um is also very important. Fields Cereal vol. tested % jnfec, tested % infec, winter 1988 15 94 10 100 winter 1989 14 90 12 80 M.äili- Samples from maize fields are still to be processed. Apterous nymphs caught in maize fields at the end of the season turned to be infective. - Infectivity of cereal alate aphids. Alates colonizing winter cereal crops. In the autumn of 1987 15% of alates arriving at the crop were infective. In autumn 1988, 31% of alates were infective. - 79 - alates caught % infective ....§.§._ --8..!L ....§.§._ .....B..ll autumn 1987 8 25 0 20 autumn 1988 18 137 0 32 Alates colonizing maize. In the spring of 1988, 28% of alates arriving at maize were infective. alates caught % infe!;,tive ....§.§._ --8IL.. � -1m spring 1988 43 98 4 38 The latest samples, tested against Harpenden Laboratory monoclonal antibodies, seem to show that PAV is the predominant isolate. 4,- Discussion and future research. 1) In our area BYDV is maintained on the different cereal aphid hosts all over the year. Alate aphids colonizing winter cereal. and maize have shown to be infective in a significant rate. Consequently factors affecting aphid population dynamics through the different crops should to be considerably important in the widespreading of the disease. Forage cereals seem to have special importance as an aphid host since this crop has always been found to be infected in a high rate not depending on the year considerated. Although the surface devoted to forage cereal (usually associated with vetch) is not very large it is widely distributed all over the region. 2) Most of the infective alate aphids colonizing winter cereal in autumn are R.padi. This fact and the consideration that R.padi is always the predominant species arriving at winter cereal points to the prevailing role of R.padi as the main cause for BYDV inocculum spreading over winter cereal. 3) R.padi survival on winter cereal depends on the hardiness of the winter. Mild winters allow R.padi populations to be maintained through the winter on winter cereal and in spring the increase of population could be very high and therefore the transmission of BYDV to maize. 4) In severe winters S.avenae survives better on winter cereal than R.padi. So in hard winters S.avenae is the main BYDV vector - 80 - from winter cereal to maize. The virus will be spread by R.padi from maize to winter cereal later on in the season. 5) Since PAV is transmited by both R.padi and S.avenae, the transmission of this strain is assured through the different hosts along the year in our area. According to Foxe and Rochow (1975), R.padi is more efficient in the transmission of PAV than S.avenae. This fact remarks the role of R.padi in PAV epidemiology. In spring the transmission of BYDV from winter cereal to maize is mainly due to S.avenae, specially in hard winters, so the transmission of RPV is partially broken. In autumn the transmission of BYDV from maize to winter cereal is caused mainly by R.padi, so the transmission of MAV is also partly broken. This reasoning lets us explain why PAV could be the most important strain in Spain and also in our area. This agrees with the preliminar results obtained using Harpenden Laboratory monoclonals. Although further studies should to be done to confirm this preliminar hypothesis. 6) In the next future studies should be done to assess the importance of long distance aphid migrations. Such studies could partially modifie this pattern. REFERENCES ANONYMOUS. 1987. Anuario de Estadistica Agraria. Ministerio de Agricultura Pesca y Alimentaci6n. Madrid. COMAS,J.; PONS,X.; ALBAJES,R. 1989. A five year study of cereal aphid biology in Catalonia. WPRS Bull. 12(1 ), 12-16. FOXE, M.J.; ROCHOW, W.F. 1975. Importance of virus source leaves in vector specificity of barley yellow dwarf virus. Phytopatho1ogy, 65, 1124-1129. JORDA,C.; OSCA,J.M.; ALFARO,A. 1990. Barley yellow dwarf in Spain. In Burnett, P.A., ed. 1990. Wolrd perspectives on barley yellow dwarf. CIMMYT, Mexico, D.F., Mexico. pp: 45-48. LISTER,R.M; FERERES,A.; FOSTER,J.E.; CASTANERA,P. 1990. Occurence of barley yellow dwarf virus in three major cereal-growing regions of Spain. Wolrd perspectives on barley yellow dwarf. CIMMYT, Mexico, O.F., Mexico. pp: 45-48. MORIONES,E.; ORTEGO,F.; RUIZ-TAPIADOR,M.; GUTIERREZ,C.; CASTANERA,P.; GARCIA-ARENAL,F. 1989. Epidemiologia del virus del enanismo amarillo de la cebada en Espa�a. Proc. VII Congreso Nacional de Fitopatologia. Badajoz, 17-20 October 1989. - 81 - OSCA,J.M. 1990. Caracteristicas de las razas espanolas del virus del amarilleo enanizante de la cebada (BYDV). Tesis Doctoral. Universidad Politecnica de Valencia. Escuela Tecnica Superior de Ingenieros Agr6nomos. 294 pp. PONS,X.; ALBAJES,R. 1987a. Biology of BYDV vectors in wheat in Catalonia (Spain). WPRS Bull., 10(1): 36-41. PONS,X.; ALBAJES,R. 1987b. Role of corn and the vetch+cereal associated crop in BYDV vector populations in Catalonia (Spain). WPRS Bu 11 . , 10 (1 ) : 42-45. AKNOWLEDGEMENTS Thanks are due to the CICYT, which partially funded this work (Project 1174/84). - 82 - SPRINGACTIVITY ASSESSMENTOF PARASITOIDS INWESTERN FRANCE BY EXPERIMENTAL EXPOSUREOF CEREALAPIDDS ON TRAPPLANTS IN AWHEAT FIELD. C.A. DEDRYVER(l), VERONIQUE CREAcii(2),J.M. RABASSE(3) andJ.P. NENON(2) (1) INRA, Laboratoire de la Chaire de Zoologie de l'ENSAR, Domaine de la Motte, F35650 LE RHEU. (2) Laboratoire d'Entomologie fondamentale et appliquee, Universite de Renne&!, Campus de Beaulieu, F35042 RENNES Cedex. 3 ( ) INRA, Laboratoire de Biologie des Invertebres, 37 boulevard du Cap, F06602 ANTIBES. RESUME L'exposition dans un champ de ble de plantes pieges infestees par des quantites egales de Rhopalosiphum padi L., Sitobion avenae F., et Metopolophium dirhodum Wlk. a permis d'estimer l'activite de leurs parasitoi:des au printemps. Celle-ci est la plus importante de mars a debut mai, lorsque les populations de pucerons sont faibles ; le pourcentage de pucerons parasites decroit ensuite de mai juin a juillet. La principale espece d'Aphidiide est Aphidius uzbekistanicus Luz.,0dont la prefärence parasitaire et la sex ratioparaissent instables au cours du temps. Cereal aphids are commonly parasitized in the fields by Hymenoptera, mainly Aphidiids Although several methods are available for estimating levels of parasitization in the field, like aphid dissection (ROBERT, 1979; DEDRYVER & GELLE, 1982 ; DEDRYVER, 1987), aphid rearing (DEAN, 1974) or electrophoresis (HÖLLER & BRAUME, 1988 ; WALTON et al., 1990), the changes with time of aphid species composition, aphid density and repartition in the field and on the plant, make intraseasonal and between years comparisons rather difficult. As an example, some of the results (DEDRYVER, 1987 ; WALTON et al., 1990) pointed out that in oceanic areas like Western France and Southern England, cereal aphids parasitizationcan be very high at the beginning of spring. This was correlated or not with subsequent low aphid populations levels. At this period, aphids are rare in the field and more accurate methods are requested because the samples are small and not reliable. This paper reports an attempt to quantify spring activity of cereal aphids parasites in the oceanic conditions of the Rennes basin (West of France), in 1988. A method for exposing trap plant in a wheat field, similar to that developped by CAMERON et al. (1984) was used to avoid direct dependence on the field density of aphids. Parasitization of a constant sample of different aphid species was assessed from March to July. In addition, it was possible to study more accurately some components of parasite biology like host preference and sex-ratio. MATERIALSMETHODS AND . Assessmentof the primaryparasites activity A standard exposure unit (S.E.U.) consisted in a pot, 10 cm in diameter, containing 25 wheat seedlings (cv. Arminda) infested by an equal number of aphids of the 3 species Rhopalosiphum padi L., Sitobion avenae F. and Metopolophium dirhodum Wlk. Aphids were obtained from laboratory cultures reared at 20°C, L16 : D8. The experiments were done in a winter wheat field (cv. Arminda) near LE RHEU (INRAExp. Stn. ofRennes) at 6 to 9 exposure locations 10 x 10 m distantfrom each others. A first succession of experiments (23/3, 30/3, 8/4, 13/4, 21/4, 28/4, 4/5) consisted in a 24 h exposition of one S.E.U. in each of the nine locations at the canopy level, with 30 second instar larvae ofeach aphid species per S.E. U .. During a second succession of experiments, two different S.E.U. were exposed at the canopy level during 24-36 h on each of 6 locations : one consisted in 20 second instar larvae of each species per wheat pot, the second in 20 fourth - 84 - 1001 40 35 ... 30 p 1001 � 25 1 1001 561 � 20 E A 15 p 131 1 D 10 1001 lOOI s Eil:w.:tl: Percentages of parasitized aphids in the S.E. U. ( •1 ) with standard Deviation, and percentage of S.E.U. with parasitized aphids (%) foreach date of experiment. SITOBION AVENAE 60 35 50 30 40 .% 25 PARASITISM INTHE S.E.U 20 30 • %MUMMIES • INTHEFIELD APHIO 15 POPULATION 20 10 24/3 814 22/4 4/5 2415 14J6 30/6 TIME �: Mean numbers of S. avenae per sample of 20 tillers in the wheat field (-) with associated percentages of mummies at field ( • ) and percentages of S. avenae parasitizedin the S.E.U. ( a ), - 85 - instar larvae ofeac h species. Twelve experiments were done, grouped by series of 3-4 consecutive days (23, 24, 25/5 ; 8, 9, 10/6 ; 21, 23, 24/6 ; 7, 9, 10/7). For each experiment the results concerning the 2 S.E.U. were finally pooled together, no significant differencebeing found between parasitization ofyoung and old larvae. After the field exposition, S.E.U. were brought back to the laboratory for aphid loss assessment ; then the pots were covered with a cellophane bag and placed outdoors, under shelter. Mummification was daily checked and mummies were individually tubed and kept outdoors. Emergences were observed daily. The shelter temperature was registered during the whole experiment. Finally adult parasitoids and theiraphi d hosts were identified in the laboratory. . Sampling thefi eld populations of cereal aphids Living cereal aphids and mummies were sampled and visually identified weekly in the wheat field from March 23rd to the end of July on 50 to 10 batches (depending on aphid density) of 20 consecutive tillers. The batches were 10 x 10 meters distant from each other in the field. . Statistical analysis were achieved using the package STAT-ITCF version 5 (TRANCHEFORT et al., 1987). RESULTS * Assessment ofparasitism and comparison with aphid populations in the field. For the whole period of experiment 922 mummies were collected in the S.E.U., 85.7 % of the emerged adult primary parasitoids were A. uzbekistanicus. The other species were Aphidius matricariae HAL. (6.4 % ofthe emerged adults), Aphidius picipes NEES (2 % of the emerged adults) and Praon sp. (0.5 %). One specimen of Aphidius ervi HAL. emerged. The parasites died in 5.4 % of the mummies. Percentages of parasitism were calculated for each date, taking into account the loss of aphids during the exposition time. Figure 1 shows large variations between days and between weeks of experiment. In March and April there were no parasitism at all on April 8th and less than 1 % on April 28th, but up to 31 % on April 13th which is the higher mean level of parasitism recorded during all the experimental period. In May and June there is evidence of large between days variations. More generally, the level of parasitism appears cahotic at the beginning of spring, then increase between the end of May and beginning of June and finally decrease in June to become very low at the end of June and - 86 - D.F. = 12 T MIN. T MAX.T MEAN. INSOL. RAD. RAIN. HUME. Day preceding the exposition -0.2S 0.03 -0.096 0.600 0.550 -0.534 -0.184 ofthe S.E.U. * * * Dayofthe exposition of -0.161 0.138 0.007 0.540 0.550 -0.098 -0.041 the S.E.U. * * Tabk; 1 : Coefficient of correlation between the percentage of parasitized aphids in the S.E.U. and some climatic data: T MIN.: minimal dailytemperature (°C); T MAX. : maximal daily temperature (°C) ; T MEAN: mean daily temperature (°C) ; INSOL : daily insolation (in hours) ; RAD. ; daily radiance (in mega J/m2) ; RAIN : daily rainfall (in mm.) ; HUME : daily humectation (in hours) (* significant: 0( <0.05) S. avenae M. dirhodum R. padi 2 A. uzbekistanicus 384 227 278 20.47 *** A. picipes 13 5 0 8.27 ** A. matricariae 22 2 33 25.99 *** Tabl� 2 : Number of A uzbekistanicus, A. picipes and A. matricariae emerged from the different:aphid species from the S.E.U. and relevant X.2 homogeneity tests. (** P < 0.01 ; *** P < 0.001). - 87 - beginning of July. Three main peaks of activity for parasitoi"ds appear on Figure 1: mid-April, beginning ofMay and beginning ofJune. Figure 2 represents for S. avenae, the total field population with percentage ofmummified aphids in the field, and percentage ofparasitism in the S.E.U.. The periods of maximal efficiency of parasitoids as measured by both methods correspond to some extend. The parasitoids appeared very efficient between April and beginning of May when aphid populations is very low. At the peak of the aphid population, levels of parasitism were lower than 5 % in the S.E.U.. The relationship between daily percentages of parasitism in the S.E.U. and climatic factors is shown on table 1. The only significant correlations were found with insolation and radiance ofthe exposition day ofthe S.E.U. and for the preceding days (in positive) and for the rainfallof the preceding day (in negative). * Parasitismof the differentaphid species Total numbers of adults of the 3 main parasitoid species emerged from each aphid species are shown on table 2. S. avenae was more parasitized by A. uzbekistanicus than R. padi and M. dirhodum.A. picipeseme rged mainly from S. avenae and no R. padi parasitized by this species was found. A. matricariae emerged more from R. padi than from S. avenae. A very low number of M. dirlwdumwas parasitized by this species. Moreover figure 3 shows a change with time of the preferences of the more abundant parasitoid, A. uzbekistanicus. At the beginning of the spring, R. padi was more parasitized than the other species (all mummies collected on rd March 23 were R. padi). From mid April to the beginning of May, 50 % of the parasitized aphids were S. avenae and from the end of May to the beginning of June the 3 species were equally parasitized. At the end of June S. avenae was clearly less parasitized than both other species. Figure 4 shows a linear relationship and a significant correlation between the percentage of each aphid species in the field and its percentage in the relevant mummy sample from S.E.U .. Larger was the relative importance of one species in the field, more this species seemed prefered in the S.E.U .. * Sex-ratioofthe parasites The sex-ratio of A. uzbekistanicus was calculated for the 4 larger samples from the S.E.U .. lt reached approximately 1/1 for the 3 first dates of th sampling and 60 females/40 males on June 10 . The sex-ratio differed with the aphid host (figure 5) being more stable and higher for parasitoids emerging from - 88 - p 127 70 E 100 lJ 10] 79 314 •• R C 90 E N 80 T A 70 G E 60 III S.AVENAE 1i1 M.DIRHODUM 0 50 F !IQ A.PADI 40 T H 30 E 20 T 0 10 T A 0 L 23:03 30:03 13:04 21:04 04:05 22:05 • 07:06 22:06 TIME �: Percentages of the 3 aphid species in the A uzbekistanicus mummies sample at each date of experiment, with the size of the sample (numbers). p 60 R 0 p p A 0 R 50 R A T s 1 1 • ll .. 0 T 40 ... N E D • S.AVENAE 0 • M.DIRHODUM F 30 � E • A.PADI A T - REGRESSION C H l!J „ LINE (R=0.7) H E 20 s s p • E E 10 ü ?E s 0... -..--..--..--..--..--..--...--..--...---. 0 10 20 30 40 50 60 70 80 90 ,oo PROPORTION OF THE DIFFERENT SPECIES IN THE FIELD �: Relationship between the population of each aphid species in the fieldand the correspondingproportion of each aphid epeciea in the mummy sample of the S.E.U. - 89 - S. avenae (50-60 % females) than fromR. padi (40-52 % females). The sex-ratio of parasitoids emerging from M. dirhodum appeared very unconstant and increases with time(41 % femaleson April 14th to 72.5 % on June 10th). DISCUSSION * On the method The trap-plant method used in this study, and before by CAMERONet al., (1984), was an attempt to standardize comparisons to a certain extent. lt allows to compare 24 hours parasites activity, in a posteriori precisely-known climatic conditions. lt allows also to get a more standard index for parasitoid activity, as variations in numbers, age structure and plant repartition of the aphid populations do not appear any longer. For the same reasons, its value is relative and does not express the pure reality in the field, but a potential parasitoid activity at a given time. * On the results Conceming the potential activity of parasitoi:ds in the field, two main points are obvious from our results : i) a very early and irregular activity of the parasites when aphid populations are inexistant or very low ; ii) a general decrease of the parasitism levels from the beginning of June to July, as aphid populations increase. Previous results from dissection (DEDRYVER, 1987), rearing (DEAN, 1974; VORLEY & WRATTEN, 1985) or electrophoresis (WALTON et al., 1990) of living aphids collected in the field, pointed out that, in oceanic areas, parasitism level could be very high in early spring. Our experiments confirm the possibility for parasitism to reach very high levels ( up to 35 % ) in April or May in the Rennes basin. This seems to be due to temporary high activity of the parasites, probably partly dependant of some climatic factors not systematically correlated with temperature like insolation and radiance, the importance ofwhich was until now neglected in Aphidiid behaviour studies. The role of these factors on the take-off, of insects specially aphids, is well-known (ROBERT, 1987) and STARY (1970) indicated that insolation and temperature were of major importance for Aphidiid activity. The existence at a local scale of a parasite stock when hosts are very rare in the field, could be related with the way for the parasites and aphids to overwinter in oceanic areas. Cereal aphids overwinter mainly parthenogenetically on various Gramineae in the these regions (DEDRYVER & - 90 - % FEMALES 14/4 4/5 26/5 1016 DATES A. �: Sex ratio (% of females) of the uzbekistanicus sample for the 3 species of aphids - 91 - GELLE, 1982) and their parasites develop continuously in their hosts during winter without diapause (KRESPI, 1990). Therefore, the reservoirs of overwintering aphids (volunteers, grasses) produce in early spring large quantities of parasites able to spread to adjacent crops when climate is temporary favourable. The role ofthese parasites could be limited in the fields by the low aphid populations and their dispersion, involving a high effort for host searching in the short time when climate is suitable. The progressive decrease fromJune to July of parasitism level was still recorded by classic field sampling (DEDRYVER, 1987 ; WALTON et al., 1990). One of the reasons can be a problem of Aphidiid disponibility caused both by hyperparasitism and by fieldabundance ofaphids. This work corroborates numerous results of field observations showing that A uzbekistanicus is the dominant cereal aphids parasitoid as in many european countries (LA'ITEUR, 1979 ; CASTANERA, 1982 ; POWELL, 1982 ; RABASSE & DEDRYVER, 1983 ; DEDRYVER, 1987). More original are the results concerningA matricariae a polyphagous species which was known to be important on R. padi in oceanic countries in early spring (RABASSE & DEDRYVER, 1982). lt appears from our experiment that this species does not parasite M. dirhodum or very few but has no clear preference between R. padi and S. avenae, which confirms some field results fromKRESPI (1990). The exposure of equal quantities of the 3 species of cereal aphids to natural parasitism allowed us to get a contribution to the field study of host preference. Our results agree partly with those of IBRAHIM (1987) who showed in the laboratory that S. avenae was preferred by A uzbekistanicus, which is generally the case in our experiments. IBRAHIM (1987) indicated too, that, after S. avenae, the next prefered species forA uzbekistanicus was its previous host. This can explain partly the change of host preference with time that we recorded, and the obvious relationship between the preference for a species and its field abundance. Particularly the preference in early spring forR. padi could be due to the high proportion of this species in the overwintering parthenogenetic aphid populationsin various reservoirs. Finally the increase with time of the sex-ratio ofA uzbekistanicus was still observed by HÖLLER (1984) who suggested some relationships with temperature. FLANDERS (1965) observed that for some species of hymenoptere, mated eggs were laid in the most suitable hosts, which could be related with our results concerning the higher and more stable sex-ratio of A. uzbekistanicus emerging fromS. avenae. - 92 - In conclusion, the role of parasitism in aphid population dynamics is a complex phenomenon that can not be explained only by field observations and laboratory trials which give very different kinds of results. The linkage between them can be done by experimental field trials in which some components of the plant-host-parasitoid system are fixed. REFERENCES CAMERON P.J., POWELL W., LOXDALE H.D., 1984. Reservoirs for Aphidius ervi Haliday (Hymenoptera : Aphidiidae), a polyphagous parasitoid of cereal aphids (Hemiptera: Aphididae). Bull. Ent. Res.H, 647-656. CASTANERA P., 1983. The relative abundance of parasites and predators of cereal aphids in central Spain . .In: Aphid Antagonists. R. Cavalloro Ed. 76- 82. DEAN G.J., 1974. Effects of parasites and predators on the cereal aphids Metopolophium dirhodum (Wlk.) and Macrosiphum avenae (F.) (Rem., Aphididae). Bull. Ent. Res. §.a, 411-422. DEDRYVER C.A., 1987. Biologie, ecologie et dynamique de population des pucerons des cereales en climat oceanique. These Doc. Sciences, Universite ParisSud (Orsay), 199 pp. DEDRYVER C.A., GELLE A., 1982. Biologie des pucerons des cereales dans l'Ouest de la France. IV. - Etude de l'hivemation de populations anholocycliques de Rhopalosiphum padi L., Metopolophium dirhodum Wlk. et Sitobion avenae F. sur repousses de cereales dans trois stations de Bretagne et du Bassin parisien.Acta Oecologica, Oecol. Applic. J, 321-342. 1 FLANDERS S.E., 1965. On the sexuality and sex-ratios of hymenopterous parasites. Amer. Naturalist, fil!, 489-494. HÖLLER C., 1984. Untersuchungen zur Biologie der Parasitoiden (Hymenoptera, Aphidiidae) der Getreideblattlause. Diplomarbeit aus der Institut für Phytopathologie, Kiel, 106 pp. HÖLLER C., BRAUME H.J., 1988. The use of isolectric focusing to assess percentage hymenopterous parasitism in aphid populations. Entomol. exp. appl. .il, 105-114. IBRAHIMA.M.A., 1986. Studies onAphidius uzbekistanicus LUZ., (Hymenoptera : Aphidiidae) parasitoid of the cereal aphids Sitobion avenae F., Metopolophium dirhodum Wlk. and Rhopalosiphum padi L. Thesis Doc. Cairo Univetsity, 194 pp. - 93 - KRESPI L., 1990. Etude de la biocenose parasitaire des pucerons des cereales dans le Bassin de Rennes : cas particulier d'Aphidius uzbekistanicus LUZ. These Doctorat Universite Rennes I., 105 pp. LATI'EUR G., 1973. Etude de la dynamique de population de pucerons des cereales. Premieres donnees relatives aux organismes aphidiphages en trois localites differentes. Parasitica �. 134-151. POWELL W., 1983. The role of parasitoids in limiting cereal aphid populations. 1nAphid antagonists . R. Cavalloro Ed. 50-56. RABASSE J.M., DEDRYVER C.A., 1982. Overwintering ofprimary parasites and hyperparasites of cereal aphids in WesternFrance. InAphid antagonists.R. Cavalloro Ed. 57-64. RABASSE J.M., DEDRYVER C.A., 1983. Biologie des pucerons des cereales dans l'ouest de la France. III - Action des hymenopteres parasites sur les populations de Sitobion avenae F., Metopolophium dirhodum Wlk. et Rhopalosiphum padi L. Agronomie, a, 779-790. ROBERT Y., 1979. Recherches ecologiques sur les pucerons Aulacorthum solani Kltb., Macrosiphum euphorbiae Thomas et Myzus persicae Sulz. dans l'Ouest de la France. III - Importance du parasitisme par hymenopteres Aphidiidae et par Entomophthora sur pommes de terre. Ann. Zool. Ecol. anim., ll, 371-388. ROBERT Y., 1987. Dispersion and migration. In : Aphids, their biology, natural ennemies and control (Vol 2A). A.K. Minks & P. Harrewijn (Eds), Elsevier, Amsterdam, 299-313. STARY P., 1970. Biology of aphid parasites. Series Entomologica, Junk, den Haag, 643 pp. STARY P., 1976. Parasite spectrum and relative abundance of parasites of cereal aphids in Czechoslovakia (Hymenoptera : Aphidiidae ; Homoptera Aphidoidea). Acta entomol. bohemoslov, 1.3., 216-223. TRANC�FORT J:, BEAUX M.F., GOUET J.P., PHILIPPEAU G., VERNEAU M., 1987. STAT-ITCF. Manuel d'utilisation. I.T.C.F., PARIS. 208 pp. VORLEY W.T., WRATTEN S.D., 1985. A simulation model of the role of parasitoids in the population development of Sitobion avenae F. (Hemiptera: Aphididae) on cereals. J. appl. Ecol., 22, 813-823. WALTON M.P., POWELL W., LOXDALE H.D., ALLEN-WILLIAMS L., 1990. Electrophoresis as a tool for estimating levels of hymenopterous parasitism in field populations of the cereal aphid, Sitobion avenae. Entomol. exp. appl., M, 217-279. - 94 - Some aspects of host selection by two aphid hyperparasitoids: Asaphes vulgaris Wllc.and Asaphes suspensus(Nees) (Hymenoptera: Pteromalidae) Petra Christiansen - Weniger Institut für Phytopathologie der Universität Kiel D-2300 Kiel Summary Atteil1ptsto analyse the host selectio� pattems of Asaphes spp. are difficult be cause of their polyphagy. Females of Asaphes vulgaris and Asaphes suspen- sus, conditioned for two years on Aphidius rhopalosiphi, were first exposed to different possible selection factors before testing their preference between Aphidius rhopalosiphi (Sitobion avenae) and Aphidius ervi (Acyrthosiphon pisum). Tue first generation of the Asaphes species reared on A ervi was also tested. While Asaphes suspensuswas already stimulated by the host plant, both species accepted A. ervi better after previous feeding on this host. Obviously Asaphes spp. "leam" to accept a new host by host feeding. Tue first generation of Asaphes spp. reared on A. ervi showed a sliglit preference towards A. ervi. In host selection tests of the conditioned Asaphes spp. between A. rhopalosiphi and A. ervi, both reared on S. avenae, A.ervi was still discriminated in a similar way as A. ervi in Acyrthosiphon pisum. Methanol extractions from empty A. ervi mummies, applied to mummies of A. rhopalosiphi, led to a refusion of the "strarigesmelling" nfummy.Thcn�xperiments indicate that semiochemicals, prodriced by the primary parasitoid in mummies, are percieved by the hyperparasitoids. - 95 - Introduction Tue genus Asaphes (Hymenoptera: Pteromalidae) occurs late but in relatively !arge numbers in cereals (Jones 1979, Höller 1988). Two species are known: Asaphes vulgarisWlk. and Asaphes suspensus (Nees). Both hyperparasitoids are ecto phagous and polyphagous (Sullivan 1987). In search of a possible manipulation of host acceptance by Asaphes spp., with the aim to minimize their negative effect on the cfficiency of primary parasitoids, host se lection behaviour should be better understood. This study investigated the following questions: a) could host selection be influenced by the effect of "associative learning", as it has been reported for braconids (Vinson et al. 1977, Dmoch et al. 1985) and ichneu monids (Arthur 1971), b) which factors could be involved in this process and c) may semiochemicals be involved in host acceptance by Asaphes spp.? Methods Asaphes vulgaris and Asaphes suspensus were collected from winterwheat and reared in the laboratory for two years on Aphidius rhopalosiphi De Stefani Perez, with Sitobion avenae F. as host aphid and Avena sativa L. as host plant. Females examined in selection tests were kept as standard seven to ten days on their ° hosts from which they had emerged at a constant temperature of 20 ..±.1.5 C and a L16:D8 light - dark regime. Tue selection tests were performed in 35mm Petri dishes, in which a female hyper parasitoid was given the choice between two host species, each in three mummies. Tue number of attacks (perforation of the mummy with the ovipositor) within one hour was counted. In all tests thirty females of Asaphes vulgaris and twenty of the more active Asaphes suspensuswere studied. Selection tests of Asaphes spp. between A. rhopalosiphi (reared on S. avenae / A. sativa) and A ervi (reared on A pisum / V. faba) were carried out with: 1. females from A. rhopalosiphi cultures, - 96 - I.ahk.1. Host selection of Asaphes spp. (reared for 2 years on Aphidius rhopalo siphi with the host aphid Sitobion avenae on Avena sativa) between Aphidius rhopa/osiphi (Sitobion avenae as host aphid and Avena sativa as host plant) and Aphidius ervi (Acyrthosiphon pisum as host aphid and Vicia faba as host plant). For each replicate a female was offered 3 mummies per host species for one hour. selection test 3days mummies attacked •> % attack on species reared on exposure to offered mummies A. rhopolosiphi A. ervi Asophes A. rhopolosiphi A. rhopolosiphi- 180 53 82.4 17.6 vulgoris culture (n= 30) A. rhopalosiphi saccharose( s) only 44 70.4 29.6 Vicio /obo and (s) 47 70 .2 29.8 parasitized A. pisum 46 69.6 30 .4 (A. ervi)on Vicio /obo A. ervimummics and (s) 65 52.3 47.7 A . ervz.2) A. ervi - culture 54 38.9 61.1 Asophes A. rhopalosiphi A. rhopolosiphi- 120 46 67.4 32.6 suspensus culture (n = 20) A. rhopalosiphi saccharose( s) only 42 64.3 35.7 Vicio fobo and (s) 47 51 49 parasitized A. pisum 38 52.6 47.4 (A. ervi) on Vicio /obo A. ervi - mummies and (s) 58 43.1 56.9 2> A. ervi A. ervi - culture 39 43.6 56.4 1) mummies perforated with the ovipositor 2) first generation of Asophes spp .on Aphidius ervi - 97 - 2. females from A. rhopalosiphi cultures, exposed three days to: - saccharose solution (15%, in cotton wool) only in a Petri dish, - Viciafaba in a plexiglass tube (30cm x 10cm) with additional saccharose, - Vicia faba with parasitized, not yet mummified A. pisum (A. ervi) without additional saccharose, - mummies of A. ervi in a Petri dish with additional saccharose, 3. females developed in the first generation on A. ervi. Tue selection of Asaphes spp. between A. rhopalosiphi and A. ervi, both reared on S. avenae / A. sativa, should provide an indication if the primary parastoid plays a role in the selection process. To test if semiochemicals emitted by the host may be involved, 100 empty mummies of Aphidius ervi (Acyrthosiphon pisum) were transferred each into Eppendorf reaction tubes and extracted with 100 pi me thanol (99.8 %). After centrifugation at 12.000 rpm for 10 minutes, the supernatant was used: 1 J1lwas pipetted on each A. rhopalosiphi mummy. On the total 150 mummies were treated in this way. As control, the same number of A. rhopalo siphi mummies was treated with lµl methanol (99.8 %) only. In order to examine the antagonistic potential alld life duration of both Asaphes species, thirty fresh mummies of A. rhopalosiphiwere offered daily to a female in a Petri dish. Mummies from which llO Asaphes offsprillg had emerged were dis sected. Unhatched eggs of Asaphes spp. call easily be recogllized,because their residue is still anchored in the deteriorated host. Mummies killed by oviposition can thus be distinguished from mummies killed by host feeding. Resultsal ld djscussion Tue conditionillg of Asaphes vulgaris Oll A. rhopalosiphi was reflected in a strong preference towards A. rhopalosiphi (Tab.1). lt was, however, partially di millished, when, three days before the selection test, the females were exposed to saccharose ollly. Previous "experiellce" Oll the host plant of A. ervi: Vicia faba and the host aphid A. pisum, parasitized by A. ervi, still led to a discrimillatiollof A. ervi. By colltrast,attack rate on A. ervi was considerably illcreased, whell Asa phes vulgariswas given the possibility to feed on A. ervi before. Tue first genera tion of Asaphes vulgaris reared Oll A. ervi preferred A. ervi. - 98 - Higher tolerance towards "strange" hosts, often observed in Asaphes suspensus, was also rnanifestedin the test (Tab.l). A. ervi was rnorereadily accepted as host, when Asaphes suspensuswas previously exposed to Vicia faba. Honey dew re leased by parasitized A. pisum on the sarneplant had obviously no further effect on the attraction rate. Host feeding on A. ervi again enhanced host acceptance of this species. The first generation of Asaphes suspensus, reared on A. ervi, preferred A. ervi to a lesser degree than Asaphes vulgaris. The low attack rate of the Asaphes species on A. ervi (Tab.2) indicates that the primary parasitoid is an irnportantfactor in host recognition. This is further supported by the fact that the strongest influence on the acceptance of the "new host" A. ervi was obtained after a prior contact with this host (Tab.l). Host acceptance by Asa phes suspensusafter previous contact with the host plant Vicia faba only (Tab.1), without any experience on A. ervi, could be interpreted as stirnulatedsear chine behaviour. Iahk.2.Host selection of Asaphes spp. (reared for 2 years on Aphidius rho palosiphi with the host aphid Sitobion avenae on Avenasativa) between Aphidius rhopalosiphiand Aphidius ervi with the host aphid S. avenae on A. sativa. For each replicate a fernalewas offered 3 rnurnrnies'per host species for one hour. murnrnies attacked % attack on species offered rnurnmies A. rhopalosiphi A. ervi Asaphes 180 60 63.3 36.7 vulgaris (n=30) Asaphes 120 40 77.5 22.5 suspensus (n=20) The methanol extracts of empty A. ervi mummies, applied to the preferred A. rho palosiphi mummies, led to an irritation of the hyperparasitoids (Tab.3). These re- - 99 - sults, as weil as those represented in Table 2, indicate that semiochemicals, pro duced by the primary parasitoid within the mummies, are involved in the selection process. Table 3. Host selection of Asaphes spp. (reared for 2 years on Aphidius rho pa/osiphi with the host aphid Sitobion avenae on Avena sativa) between Aphidius rhopalosiphi, treated with 1 ul methanol (control) and Aphidius rho palosiphi, treated with 1 µl methanol extract, derived from Aphidius ervi mummies. For each replicate a female was offered 3 mummies per host species for one hour. mummies attacked % attack on A. rhopalosiphi species offered mummies methanol only methanol extract Asaphes 180 44 70.5 29.5 vulgaris (n=30) Asaphes 120 39 69.2 30.8 suspensus (n=20) Host feeding of Asaphes lucens (Provancher), which is presumably identical with Asaphes suspensus(Höller, personal communication), was described by Keller and Sullivan (1976 ). Its influence on the antagonistic potential of Asaphes spp. is impressing: one third of killed mummies are due to host feeding alone (Tab.4 ). Table 4. Life duration of Asaphes spp., exposed to saccharose and 30 fresh mummies of Aphidius rhopalosiphi (renewed daily), and number of A. rho palosiphi, killed by oviposition and host feeding alone. mean life duration no. of A. rhopalosiphi killed by % species (days) (n=5) oviposition and host feeding host feeding Asaphes 46 (SD=9) 278 (SD=80) 144 (SD=34) 34.1 vulgaris Asaphes 62 (SD=l3) 440 (SD=74) 167 (SD=63) 27.5 suspensus - 100 - Tue results of the selection tests in Table 1 indicate that host feeding plays an im portantrole in the parasitic behaviour of these hyperparasitoids: they show an appa rent change in attack behaviour due to experience, i.e. chemical and physical cues in host recognition by Asaphes spp. seem to be less determined by instinct than by associative learning. Feeding on the haemolymph of the host obviously overrides the repellent effect of the A. ervi semiochemicals. In the field it seems likely that the ge nus Asaphes concentrates on the most abundant host species. This behavioµr has been termed "switching" by Murdoch (1969) and it can be expected that the two Asaphes species are not only able to switch between hosts in one, but also in diffe rent habitats. Acknowledgements I thank Prof. Dr. U. Wyss and Dr. C. Höller for comments. References Arthur, A.P., 1971. Associative learning by Nemeritis canescens (Hymenoptera: Ichneumonidae). Can. Entomologist 103: 1137 - 1141. Dmoch, J., Lewis, W.J., Martin, P.B. & D.A. Nordlund, 1985. Role of host-produced stimuli and learning in host selection behavior of Cotesia ( =Apanteles) marginiventris (Cresson). J. of Chem. Ecol. 11(4): 453 - 463. Höller, C., 1988. Effizienzanalyse der Parasitoiden an Getreideblattläusen. Dissertation Universität Kiel, 114 pp Jones, M., 1979. Abundance of aphlds on cereals from before 1973 to 1977. J. of appl. Ecol. 16: 1 - 22. Keller, L.J. & D.J. Sullivan, 1976. Oviposition behavior and host feeding of Asaphes lucens an aphid hyperparsitoid.New York Ent. Soc. 84 (3): 206 - 211. - 101 - Murdoch, W.W., 1969. Switching in general predators: experiments on predator specificity and stability of prey populations. Ecol. Monographs 39: 335 - 354. Sullivan, D.J., 1987. Insect hyperparasitism. Ann. Rev. Entomol. 32: 49 - 70 Vinson, S.B., Barfield, C.S. & R.D. Henson, 1977. Oviposition behaviour of Bracon mellitor, a parasitoid of the boll weevil (Anthonomus grandis). 11.Associative learning. Physiol. Entomol. 2: 157 - 164 - 102 - SURVEY FOR NATURAL ENEHIES OF DIURAPHIS NOXIA (MORDVILKO) IN EURASIA F. GRUBER, T. J. POPRAWSKI and E. REY UNITED STATES DEPARTMENT OF AGRICULTURE, AGRICULTURAL RESEARCH SERVICE INTERNATIONAL ACTIVITIES, EUROPEAN PARASITE LABORATORY 13-17 Rue de la Masse, F-78910, Orgerus-Bihoust, France Summary Diuraphis noxia (Mordvilko) (Homoptera: Aphididae) was detected in the Texas Pandhandle in March 1986. In less than four years, the "Russian wheat aphid" (RWA) has spread to 17 American States and 3 Canadian provinces located west of the 98th meridian. The economic loss resulting from RWA damage to wheat and barley in the United States alone has exceeded 200 million dollars in 1989. In 1988 and 1989, scientists from the European Parasite Laboratory {EPL) have collected parasitoids, predators and pathogens associated with RWA in Eurasia. Intensive field surveys in Turkey, Greece, Yugoslavia, Bulgaria, Morocco, Spain, southern France and the USSR (Moldavia, Crimea, Ukraine and Kirgizia) have resulted in the recovery of several species of parasitoids including Aphelinus sp., A· asychis Walker, A. varipes Foerster, Aphidius sp., A. matricariae Haliday, A· rhopalosiphi De Stefani, !:..· uzce.�istanicus Luzhetski, Diaeretiella rapae M'Intosh, Ephedrus plagiator Nees, Praon sp., � necans Mac kauer and P. volucre Haliday. Predators included Adonia TiITi)padamia) variegi°ta (Goeze), Coccinella septempunctat� Chrysopa � Stephens, Hippodamia tredecimpunctata L., Leucopis sp., Propylea quatuordecimpunctata L., Scymnus sp., �· � (F.), �· frontalis F. and Thea vigintiduopunctata L. Syrphidae, Staphylinidae and Chamaemyiidae were also recovered from RWA-infested plants but attempts to rear them failed. Conidiobolus obscurus (Ha 11 & Dunn) Remaudi�re & Keller, Ent.-omophthora planchoniana Cornu, Pandora neoaphidis (Remaudi�re & Hennebert) Humber, Neozygites fresenii (Nowakowski) Remaudi�re & Keller and Zoophthora radicans (Brefeld) Batko were among the entomopathogenic fungi isolated from D. noxia. The predators and parasitoids found associated with RWA ;ere freed of unwanted organisms, increased in numbers and subsequently shipped to the United States for mass production and field releases. Further surveys to collect more entomophages of RWA are planned in various regions of Eurasia including Iran, Iraq, Pakistan, Afghanistan, Yugcslavia, Turkey, France, Greece, Morocco, Tunisia, the Transcaucasus, northwes tern China and the Soviet Central Asia. 1.1 Introduction The Russian wheat aphid, Diuraphis noxia, has been described by Mordvilko (1914) from specimens collected during massive outbreaks in the small grain-growing plains of the Ukraine. - 103 - RWA is believed to originate from the Transcaucasus or/and the Tien Shan and it probably spread to its present Eurasian range with caravans, Although outbreaks of RWA occurred in Anatolia in the early 1960' s (M. Oner and C. Oncüer, pers. commun.), at present the aphid is only a sporadic pest of wheat and barley in the Mediterranean, Black and Caspian Sea basins, and the Soviet Central Asia including the Tien Shan mountains. lt is believed that RWA is rarely an important pest in Eurasia because of a combination of limiting factors including tolerant host plants, geoclimatic conditions and especially well-adapted natural enemies. Recently however, RWA has increased its distribution range to new regions of the world in which it quickly became the most important pest of small grains. Detected in the Orange Free State in the spring of 1978, D. noxia had migrated to virtually every wheat-growing area of South Africa by 1981 (Walters et al. 1980). Previously unobserved symptoms of damage by RWA were observed in Mexico in 1980 and, two years later, RWA was widely distributed in cereals on the Central Plateau, and in the Toluca and Saltillo regions in 1983 (Gilchrist et al. 1984). In 1986 the aphid was found in the Texas Pandhandle and, in less than four years, it has spread to 17 American States and 3 Canadian provinces (Lesser and Morrison 1986, Stoetzel 1987, Halbert et al. 1988, Jones et al. 1989). In general, D. noxia has prospered in semi-arid, dry land wheat regions, and its No�th American distribution range appears to be limited to the west of the 98th meridian. Control of RWA at present centers largely on the use of insecticides but long term management approaches are desired, including host plant resistance and biological control (Burton 1988). Efforts to identify natural enemies associated with RWA have been undertaken in USSR (Berest 1980), South Yemen (Erdelen 1981, Stary and Erdelen 1982), Ethiopia (Haile and Megenasa 1987) and South Africa (Aalbersberg et al. 1988, Hughes 1988). Laboratory studies in the United States have indicated that two native parasitoids species, Lysiphlebus testaceipes Cresson (Aphidiidae) and Aphelinus varipes Foerster (Aphelinidae) are poorly adapted to RWA (Gilstrap and McKinnon 1988). In March 1988, the European Parasite Laboratory has therefore redirected some of its foreign exploration to include the RWA and its natural enemies. As a result of these efforts, biological control of the aphid has been and is being a research area with encouraging results. Explorers searching for biocontrol agents of the pest have been successful in finding promising biomaterial in Eurasia. The findings of the EPL and of its cooperators are reported herein. 1.2 Methods 1988 - The search for RWA and its natural enemies was originally scheduled for southwestern USSR but the small grain growing season was too far advanced in May to complete arrangements for exploratory field work. Surveys were then shifted to southeastern Europe and Turkey because D. noxia bad been recorded in the region of Sofia (D. Kontev, person. commun,) and the areas of Egredir, Malatya, Ankara and Konya (C. Oncüer and M. Oner, person. commun ; Tuatay and Remaudi�re 1964) and because Turkey is believed to be part of the aboriginal home cf the aphid (V. Eastop, person. commun.). FG and TJP searched for D, noxia in Yugoslavia, Greece, Bulgaria, - 104 - western Turkey and central Anatolia during May 9 to June 1. K. Carl (Commonwealth Institute for Biological Control) and V. Eastop (British Museum) searched for the aphid from May 22 to June 2 in sites of western and central Turkey not explored by FG and TJP, and in southeastern Turkey near the Syrian border. FG and TJP returned to western Turkey during June 14-19. This cooperation made it possible to discover the pest and several of its biotic control agents in the first season of a new program which is considered unusual in this type of research. FG collected cereal aphids and their enemies in the French Dr6me and Vaucluse departments on two occasions: July 5-7 and August 2-5. R. Carruthers (US Department of Agriculture) and TJP surveyed western Turkey again in early September. 1989 - FG and R. Bennett (US Department of Agriculture) searched barley and wheat fields in northern and central Spain from March 28 to April 7. A. Sekkat {Ecole Nationale d'Agriculture de Mekn�s, Morocco) and R. Miller (International Center for Agricultural Research in the Dry Areas, Alepo, Syria) informed the EPL that RWA had been detected in February 1989 near Settat and Mekn�s, Morocco. FG and G. Mercadier (EPL) thus searched the northern slope of the middle Atlas during April 21 to 30. Strategies developed by the Agricultural Research Service of the US Department of Agriculture for exploring in a rational manner included international cooperative efforts which climaxed, in 1989, in the establishment of the first Joint US-Soviet Biocontrol Laboratory at Kishinev, Moldavian SSR. FG, TJP and I. Kiriac (All-Union Research Institute of Biological Methods in Agriculture, Kishinev) surveyed Moldavia for RWA during May 25 to June 15 under the auspices of the joint US-USSR program. In mid-July, Kiriac searched the region of Kishinev where he had detected RWA in 1982. Southern France was added to the list warranting exploration on the basis of the information received from French entomologists. Mercadier and K. Hopper (EPL) surveyed small grain fields in the Antibes area and the Alpes Maritimes from June 5 to 9 and again from June 19 to 22. FG explored the Alpes Maritimes and Hautes Alpes during July 3 to 8. TJP and Kiriac surveyed the Tien Shan range of the Kirghiz SSR from August 15 to September 16. A second exploration of the Moldavian SSR and a first v1s1t to southern Ukraine including the Crimean Peninsula were made from October 21 to November 8 by FG, Kiriac and S. Halbert (University of Idaho). 1.3.1 Results of surveys (Tables l to 3) 1988 - RWA were not found in Yugoslavia, Greece nor Bulgaria. The first expedition to Turkey (TJP and FG) was unsuccessful. Although not detected by them in southern Turkey, Eastop and Karl found RWA but no natural enemies in a few fields along the transect Sivas-Ankara-Ayas-Beypazari. Visual inspection of wheat (at Ayas) and barley (at Beypazari) by TJP and FG (second trip to Turkey) resulted in the recovery of RWA and natural enemies, inc luding the predatory larvae of Chrysopidae, Syrphidae, Scymnus spp. (Coccinellidae) and Leucopis spp. (Chamaemyiidae), and the adults of the coccinellids Scymnus frontalis, - 105 - Adonia variegata and Propylea 14-punctata. Ephedrus plagiator, Aphelinus spp., Aphelinus varipes, Aphidius sp., Aphidius matricariae, !· rhopalosiphi and A. uzbekistanicus were among the species recovered from parasitized D. ;oxia nymphs and adults. Aphidius spp. were also recovered fr0m the cereal aphids Sipha (Rungsia) sp., Rhopalosiphum maidis Fitch and Sitobion avenae F. found on plants infested with D. noxia. The latter parasites�collected because their hosts generally ocrn in mixed populations in the fields and because of their apparent broad hast range in the small grain ecosystem. Table 1. Primary parasites of D. noxia recovered in 1988-1989 Location Number of Number of parasites* s _ _ _ _ "" ""',______...... ,.""'"'" _ _s_n""' _ _ _ _ ...""' ,..e"";;..;'"" "" ,,..;..c..------and date aphid Aphelinus Aphidiu iaeret i 11ag Ep hedrus Praon collected 1988 Turkey June 2000 43cdef zh 1989 Morocco April 20 Moldavia May-June 1000 30b sof 4i France June 1675 z3ab 8of 70 France July 140 3a 5ef 4 1h zj Kirghizia Aug-Sept. 969 2sb s8f 4 Ukraine Oct.-Nov. 163 4b 5 lj a asychis, b varipes, c matricariae, d rhopalosiphi, e uzbekistanicus sp., f Aphidius sp., g rapae, h plagiator, i necans, J volucre. * Number of v1able adults that emerged in the laboratory, not number of mummies collected in the field. Along th is 1 ine, FG' s two surveys in the DrOme and Vaucluse French departments yielded the cereal aphid parasites Aphidius spp., Praon gallicum Stary, Ephedrus plagiator and !• varipes. All paras1tes recovered from cereal aphids other than RWA were multiplied on RWA at the EPL before shipment to the US. Coccinella 7-punctata ( pupae), Scymnus � and �· ferrugatus (larvae and adults), Adalia bipunctata and Propylea 14-punctata (adults) were among the coccinellids collected during FG's surveys in France. Diuraphis noxia was not recovered from stubble nor from dried-out wild Poaceae searched by TJP and R. Carruthers at Beypazari and Ayas in early September. - 106 - 1989 - Although D. noxia had been recorded in several regions of Spain (Castanera and S�tiago 1983; J. M. Nieto Nafria and X. Pons, pers. cormnun.), FG and R. Bennett found no RWA during extensive searches in northern and central Spain. Aphidius spp. and Ephedrus la�iator recovered from Sitobion � and Metopolophium dirhodum (Walk. f did not accept RWA as a host in a series of laboratory trials. A few unparasitized RWA were collected in late April from winter wheat in the Settat area (Morocco). Over 95% of these aphids subsequently died from fungal infection (Pando.ra neoaphidis) in the laboratory. The collapse of field populations of RWA observed in April apparently resulted from the heavy rains of March. No RWA were found in Spain on the return trip to the laboratory. Table 2. Predators of Diuraphis noxia recovered in 1988-1989 Location Number of predators and date a b c d e Scymnus Other 1988 Turkey 14 21 15 Leucopis 1989 Moldavia 210 81 13 12 Syrphidae, Chrysopidae France 37 22 5 .- Scymnus larv. Syrp., Chrys. Kirghizia 207 580 28 Syrphidae Crimea 28 8 8 21 7 Chamaemyiidae a Coccinella septempunctata, b Adonia variegata, c Propylea quatuordecimpunctata d Hippodamia tredecimpunctata, e Thea vigintiduopunctata, f Scymnus frontalis. RWA and its enemies were found in the vicinity of the Moldavian southern towns of Komrat, Suvorovo, Tchadyn-Lunga, Dubossory and Grigoriopol, and sporadically in the Soroki and Edintski regions in the north of the republic. Mumrnies of Praon �. !'..· volucre, Aphelinus sp. ( probably varipes), Ephedrus sp. and Aphid ius spp. ( probably rhopalosiph i and uzbekistanicus) were collected from RWA-infested plants. Between 80% and 95% of these murmnies were hyperparasitized. The viable primary parasites that emerged in the laboratory are accounted for in Table 1. Adonia variegata, f.• 7-punctata, P. 14-punctata and H. 13-punctata were found associated with �- noxia. RWA-infested experimental fields located some 10 km NE of Antibes, France, yielded !!• asychis, !!· varipes, �- rapae and Aphidius sp. Pandora neoaphidis was also isolated frorn RWA during the two June surveys in southeastern France. Diaeretiella rapae, !• plagiator, !'..· volucre, !!• asychis, Aphidius sp. and !!· uzbekistanicus were reared from RWA found by FG during his July visit to barley fields in the French Hautes Alpes and Alpes Mat"itirnes (Tables 1 and 3). Coccinella 7-punctata, !!• variegata, !'..• 14-punctata, larvae of syrphid flies and Entornophthorales were comrnonly found during these three surveys. - 107 - High populations of RWA were observed in several localities of the Kirghiz Tien Shan range, including Naryn, Chaek, Iachmen, Min-Kouch, Mink-Boulak and Kochkorka. Aphelinus varipes, Aphidius sp. and �· rapae were reared from murmnified RWA. No entomophthorales were found but C. 7-punctata, !!· variegata and H. 13-punctata appeared to be the key control agents of the pest in the adverse environment of the Soviet Central Asian republic. Only light infestations of RWA in winter wheat and volunteer grain were observed in autumn in Moldavia (Komrat, Surovoro), southern Ukraine (Kherson and Odessa) and Crimea ( Simferopol). A few specimens of A. varipes, �· rapae and Praon sp. were obtained from RWA collected in Crimea. Five species of coccinellids and unidentified chamaemyiid larvae were found in the Crimean fields (Table 2), During 1989 the EPL also received �- rapae, Aphidius colemani Viereck and Praon sp. obtained from RWA by Miller in Syria (May), and Aphidius sp. and larvae of Leucopis recovered from RWA-infested plants by K. Pike and L. Tanigoshi (Washington State University) in Jordan (early June). Table 3. Primary parasites of Diuraphis noxia collected in southeastern France 1989 Location Altitude Rost Parasite species and date (m) plant Antibes 7 wheat A. as:i::chis, A, varipes 6/6 D. rapae Seranon 1092 barley A, as:i::chis 6/7 Aspremont 780 barley A, as:i::chis, D. rapae 6/8 Antibes 7 wheat A. as:i::chis, A, varipes 6/20 o. rapae St. Vallier 764 barley Aphidius sp. • 7/5 P. volucre Malamaire 1044 barley none 7/5 Grl!oli�res 1150 barley none 7/5 Veynes 875 barley Aphidius sp. 7/6 Aspremont 780 barley Aphidius sp., 7/7 E. plagiator 1.3,2 Shipments Predators and parasites collected during the surveys were hand-carried or shipped to the EPL where they were quarantined and freed of any unwanted organisms. They were multiplied on RWA and finally shipped to various American governmental and university biocontrol laboratories for further multiplication, biological control studies and release in RWA-infested cereal fields. Shipments of RWA natural enemies made by the EPL in 1988-1989 are surmnarized in Table 4. - 108 - Table 4. Sunnnary of shipments of D. noxia natural enemies, 1988-89 Species shipped Origin Number shippeda PREDATORS Adonis variegata Turkey, France, Moldavia, Crimea, 719 Kirgizia Coccinella 7-punctata Crimea, Kirgizia, France, Moldavia 482 Propylea 14-punctata Crimea, France, Moldavia, Turkey 161 Thea 22-punctata Crimea, Turkey 22 Hippodamia 13-punctata Crimea, Kirgizia, Moldavia 61 Chrysopa � Jordan 30 Scymnus ater France 2 Scymnus lferrugatus?) France 7 Scymnus sp, France 17 Leucopis sp, Turkey 9 PARASITES Praon necans Moldavia 49 (äb_Jectwn?J Praon (gallicum?) France 132 Praon volucre France, Turkey 1116 �rus plagiator France, Turkey 2344 Aphelinus (varipes?) France 43 Aphelinus asychis France 3645 Aphelinus (asychis?) Moldavia 1048 Aphelinus sp. Turkey 263 Aphidius (Diaeretiella?)sp, France 752 Aphidius sp.5" Kirgizia, France, 4882 Turkey, Moldavia Diaeretiella rapae Crimea, France, Syria, Kirgizia 3316 a Combined for the two years of the surveys. b Specimens identified after shipment as Aphidius sp., A· matricariae, A· rhopalosiphi and for A. uzbekistanicus. - 109 - REFERENCES AALBERSBERG, Y. K., Van der WESTHUIZEN, M. C. and HEWITT, P. H. (1988). Natural enemies and their impact on Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae) populations. Bulletin of Entomological Research 78: 111-120. BEREST, z. L. (1980). [Parasites and predators of the aphids Brachycolus noxius and Schizaphis graminum in crops of barley and wheat in Nikolaev and Odessa regions]. Vestnik Zoologii 2: 80-81. (in Russian) BURTON, R. L., compiler (1988). The Russian wheät aphid. First Annual Report of the Agricultural Research Service, U. S. Department of Agriculture. CASTANERA, P. and SANTIAGO, C. (1983). [Study on the aphid-parasitoid (Homoptera: Aphidoidea; Hymenoptera: Aphidiidae) relationship, in the Iberian Peninsula]. Actas del Primer Congreso Iberico de Entomologia, Leon, Espana (7-10 Junio): 149-157. (in Spanish) ERDELEN, C. (1981). [The aphid fauna of the Arab Republic of Yemen, with special regard to the most important species on cereals]. Dissertation, University of Bonn. (in German) GILCHRIST, L. I., RODRIGUEZ, R. and BURNETT, P. A. (1984). The extent of Freestate streak and Diuraphis noxia in Mexico, pp. 157-163. In Barley Yellow Dwarf: Proceedings of the Workshop sponsored by the United Nations Development Programme and CIMMYT, 6-8 Dec. 1983, CIMMYT, Mexico. GILSTRAP, F. E. and McKINNON, L. K. (1988). Response of native parasites to Russian wheat aphid. Texas Agricultural Experimental Station Publication PR-4558. HAILE, A. and MEGENASA, T. (1987). Survey of aphids on barley in parts of Shewa, Welo and Tigrai, Eth iopia. Ethiopian Journal of Agricultural Sciences 9: 39-53. HUGUES, i: D. (1988). A synopsis of information on the Russian wheat aphid, Diuraphis noxia (Mordwilko). Division of Entomology, CSIRO Technical Paper 28. JONES, J. W., BYERS, J. R., BUTTS, A. and HARRIS, J. L. (1989). A new pest in Canada: Russian wheat aphid Diuraphis noxia (Mordvilko), (Homoptera: Aphididae). Canadian Entomologist 21: 623-624. LESER, J. F. and MORRISON, W. P. (1986). Texas Agricultural Extension Service, Focus on Entomology 21. STARY, P. and ERDELEN, C. H. (1982). Aphid parasitoids (Hymenoptera: Aphidiidae, Aphelinidae) from North Yemen. Entornophaga 27:105-108. STOETZEL, M. B. (1987). Information on and identific:i'tion of Diuraphis noxia (Homoptera : Aphididae) and other aphid species colonizing leaves of wheat and barley in the United States. Journal of Econornic Entomology 80: 696-704. TUATAY, N. and REMAUDIERE, G. (1964). Premil';re contribution au catalogue des Aphididae (Horn.) de la Turquie. Revue de Pathologie V�g�tale et d'Entornologie Agricole de France 43: 243-278. WALTERS, M. C., PENN, F., DU TOIT, F., BOTHA, T. C., AALBERSBERG, K., HEWITT, P. H. and BROODRYK, S. W. (1980). The Russian wheat aphid. Farming in South Africa, Leaflet Series: Wheat C3. - 110 - INFLUENCE OF PESTtCIOES ON THE_EPIGEAL ARTHROPOD FAUNA IN LABORATORY TESTS R.DE CLERCQ, H. CASTEELS and J. JANSSENS State Nematology and Entomology Research Station (C.L.O. - Gent) Merelbeke, Belgium Summary Five insecticides (parathion, dimethoate, phosalone, fenvalerate and pirimicarb) and three fungicides (propiconazole, fenpropimorph and prochloraz) were tested under 1aboratory conditi ons for thei r si de effects on carabids and spiders. Parathion and dimethoate show a very toxic effect on the carabids and spiders. Other tested pesticides show also a negative effect on the investigated beneficial organisms. 1. Introduction Since 1960 the increasing abundance of aphids in winter wbeat, has resulted in almost regular insecticide treatments, which has been developed in order to prevent severe yield loss, and this without considering the natural ennemies of the aphids. However, in recent years, many studies have proved the importance of predators and parasites in reducing cereal aphid numbers; in this group of benefici a 1 organisms the so-ca11 ed po lyphagous predators (Carabidae, Staphylinidae and Araneae) are very important in annual crops, because they can feed on a wi de vari ety of foods, but wi11 switch to eating aphids, whenever they have the oppOrtunity. In different field experiments in winter wheat we have already investigated the influence of the commonly used insecticides (parathion, dimethoate, pi rimicarb, phosa1 one and fenva1 erate) and fungicides (benomyl, fenpropimorph, prochloraz and propiconazole) on the polyphagous predators (3). This paper describes analogous experiments, carried out under laboratory conditions. 2. Material and methods The initial toxicities of 5 insecticides (parathion, dimethoate, phosalone, fenvalerate and pirimicarb) and 3 fungicides (propiconazole, fenpropimporph and prochloraz), commonly used in winter wheat, are investigated on 5 carabids (Bembidion lampros - 111 - Herbst, Asaphidion flavipes L. Pterostichus melanarius Illiger, Platynus. dorsalis Pontopp1dan and Amara s1m1 lis Gyllenhal) and 4 spi ders (Er, gone atra Bl ackwa 11, Bathyphantes gracil is Blackwa 11, Leptyphantes .tenu1s Blackwall and Oedothorax ap,catus Blackwall) w1th a laboratory method (2,4, 5, 6). The test cages are plastic petri-dishes (diameter 87 mm, height 16 mm) with a gauze-covered ventilation hole, 37 mm in diameter, on the top, while the bottom of the dishes has a circular gauze-covered hole in the centre, 60 mm in diameter. The test cage is filled with ± 30 gram dried pebble-stones (l-4 mm). The petri-dishes are moistened by drenching for l second in a solution of the investigated pesticide at the recommended concentration for pract ica l use. The untreated contro l cages are drenched in water for one second. The test cages are then dried at room temperature during 24 h. We obtain an even pesticide layer on the pebble-stones by drenching the bottom part of the cage for one second in a solution of the tested pesticides with following concentrations Active ingredient Concentration (%) parathion 0,02 dimethoate 0,02 pirimicarb 0,05 phosalone 0,25 fenvalerate 0,007 propiconazole 0,07 fenpropimorph 0,2 prochloraz 0, l The beneficial organisms are collected in the field by pitfall trapping; the captured carabids and spiders are held in plastic boxes, placed in a dark, cold room (± 5° C). They are fed with aphids and larvae of the house-fly and provided with water. Organisms held under these conditions can survive for up to four months with little mortality. The beneficials are acclimatised in the laboratory for at least 72 h prior testing. The beneficials are then transferred to the test cages (5 individuals each) in three replications and exposed to the freshly dried pesticide film on the little stones. For testing the initial toxicities of pesticides on Araneae, only one spider per test cage (15 replications) was used. After applying the pesticides the cages were placed on moistened filter paper, supp lying extra water for the benefici als. Food was given to the beneficial organisms every bio days. One, three, si x and n ine days after i ntroduct ion in the test cage, the number of dead predators were counted. - 112 - 3. Results The results of these l aboratory tests are given in tabe l I, II, III and IV Table I Side effects of five insecticides and three fungicides an a total of 5 tested ·carabid species, exposed to the residual action during several days Mortal ity ( in %) after : Treatment l day 3 days 6 days 9 days Untreated 0 3 12 24 Parathion 100 100 100 100 Dimethoate 91 95 95 97 Phosalone 37 84 99 99 Fenvalerate 17 68 81 88 Pirimicarb 40 65 73 76 Propiconazole 39 68 71 71 Fenpropimorph 69 81 84 84 Prochloraz 27 39 46 50 Tabl e II Mortal ity (in %) of fi ve insecti ci des and three fungicides an 5 carabid species after one (a) and three (b) days. Bembi- Asaphi- Ptero- Platynus Amara Treatment dion dion stichus dorsalis similata lampros flavi pes melana- rius Untreated a 0 0 0 0 0 b 0 13 0 0 0 Parathion a 100 100 100 100 100 b 100 100 100 100 100 Dimethoate a 100 100 100 93 60 b 100 100 100 100 73 Phosalone a 0 27 7 50 100 b 67 67 87 100 100 Fenva1 erate a 13 0 7 67 0 b 100 80 20 100 40 Pirimicarb a 73 7 0 93 27 b 100 33 0 100 93 Propico- a 20 80 33 50 10 nazole b 80 87 53 100 20 Fenpro- a 100 73 0 80 90 mimorph b 100 80 33 93 100 Prochloraz a 87 7 13 20 10 b 100 13 27 47 10 - 113 - Table III Side effects of three insecticides and one fungicide on a total of 4 tested spider species, exposed to the residual action during several days Mortality (in %) after Treatment l day 3 days 6 days 9 days Untreated 5 9 24 33 Pirimicarb 11 36 70 87 Dimethoate 30 64 93 98 Parathion 31 82 97 100 Propiconazole 0 3 24 46 Table IV Mortality (in%) of three insecticides and one fungicide an 4 spiders species after one (a) and three (b) days Treatment Erigone Bathyphantes Leptyphantes Oedothorax atra gracilis tenuis apicatus Untreated a 0 0 8 12 b 0 7 12 16 Pirimicarb a 0 30 12 0 b 20 70 44 10 Dimethoate a 13 70 17 20 40 90 50 75 Parathion a 27 70 12 13 93 90 72 73 Propico- a 0 0 0 0 nazole b 0 0 0 10 4. Discussion and conclusion 4.1. Carabidae - The results in table I demonstrate that dimethoate and parathion are most toxic and cause a reduction of the number of carabids after being exposed one day to the residues respectively for 91 % and 100 %. Analogous results were obtained by BASEDOW (l). - 114 - - One day after introduction of the beneficials the other insecticides pirimicarb, phosalone and fenvalerate cause a smaller reduction of the number of carabids by 40 %, 37 % and 17 % respectively. - The toxic side effect of the fungicide fenpropimorph (reduction by 69 % after one day) is much larger than the toxic action caused by the other fungicides propiconazole (39 %) and prochloraz (27 %). - After being exposed nine days to the respective residues, only prochloraz seems to have a little toxic side effect on the Carabidae fauna. - Taking into account the different species separately (Table II) we can conclude that the side effects of the investigated insecticides and also of the fungicides differ from species to species Pterostichus melanarius is the least sensitive species. 4. 2. fü::!!!'.!�!!� - Parathion and dimethoate show a slower action for spiders than for carabids; they cause a reduction of the number of spiders by 30-31% and 98-100%, after being exposed respectively one and nine days to the pesticide residues (Table III). Ptrimicarb also is toxic for the spiders. - The fungicides can also cause negative side effects on the spiders. - Taking into account the different species separately (Table IV), we can conclude that Bathyphantes -gracilis is rnore sensitive for the most tested pestic1des. References l. BASEDOW, T. (1987) Der Einfluss gesteigerter Bewirtschaftungsintensität im Getreidebau auf die Laufkäfer (Coleoptera, Carabidae). Mitt. Biol. Bundesanst., Land-Fortwirtsch.Berl in-Dahlem H 235 : 1-123. 2. CHIVERTON PH.(1988) Laboratory method for testing initial toxicities of pesticides to the carabid Bembidion lampros. Bulletin SROP/OILB, XI/4 : 107-110. 3. DE CLERCQ R. and CASTEELS H. (1988) On the influence of some insecticides and fungicides on the epigeal arthropod fauna in winter wheat. Proceedings of a Meeting of the ECE, Littlehampton, 25-27 November 1986, 167-170. 4. HASSAN, T. (1985) Standard methods to test side effects of pesticides on natural ennemies to insects and mites developed by the IOBC/WPRS Working Group "Pesticides and Beneficial arthropods. EPPO Bull. 15 : 214-255 - 115 - NITROGEN. PLANT GROWTH REGULATORS. PESTS AND DISEASES. AND THE ECONOMY OF GROWING WINTER WHEAT IN NORTHERN GERMANY TH. BASEDOW Institute of Phytopathology and Applied Zoology, Justus-liebig University, Ludwigstr. 23, D-6300 Giessen and A. Al-NAJJAR P. 0. Box 3307, Damaskus, Syria SUMMARY Field experiments on the economy of growing winter wheat (with oilseed rape as pre-crop) on sandy loam in Schleswig-Holstein were performed from 1982 to 1985 at 4 locations near Kiel (FRG) on plots of 12 x 200 m with 3 replicates. Additional special experiments took place on smaller plots of 12 x 12m, with 4 or 6 replicates. The occurrance of wheat diseases and of insect pests was measured weekly. The only insects of economic importance occurring were the cereal aphids. They showed an higher attack, the higher the amount of N-fertilizer given was (not significant). Chlormequat, in the ffeld, did not reduce the attack of wheat by cereal aphids significantly; in 2 of the 4 experiments, the attack by the aphids was even slightly higher in plots treated with chlormequat. In 7 experiments, fungicidal treatments were effective against mildew in 4, against Septoria nodorum in 3, against eyespot in only two cases. The take-all-disease was not influenced by any treatment. Cereal aphid control proved to be necessary and effective in 6 of 7 experiments. Grain yields were lowest at the lowest intensities, but only in 3 of 7 experiments highest at the highest intensity. Net outputs were highest at reduced nitrogen levels with full pesticide input. lt is shown, that a reduction of nitrogen input helps to reduce pesticide input. The environmental importance of the findings is discussed. 1. Introductfon Wheat is one of the most profitable agricultural crops, and farmers try to achieve maximum yields. To maximize it, a great amount of chemicals is used (nitrogen and pesticides), which have partly been shown to have undesirable environmental effects. Since the monetary input in growing wheat intensely has increased considerably, farmers are more engaged in regarding the net output of wheat production. But a comparism between different intensities is seldomly performed. So, - 116 - from 1982 to 1985 we have performed field experiments in Schleswig Holstein (FRG), to study the effects of the high chemical input on pests and diseases and on the economy of growing winter wheat (AL NAJJAR et al. 1989, BASEDOW et al. 1990). The main results are shown and discussed here. 2. Study areas and methods Studies took place near Kiel, in the district of Plön, at Passade, Lutterbek, Ratjendorf and Heikendorf, in even fields of winter wheat grown on sandy loam with winter oilseed rape as previous crop. Plots of 12 x 200m with 3 replicates were subjects of different treatments as shown in Tab. l. Table 1: Variables of the field experiments in winter wheat. All plots received an herbicidal treatment in spring. The sites lay east of Kiel (district of Plön) Variable N (kg/ha) Fungi- Chlor- Insecti- Performed atl) cides mequat cide in year P 1982/83/84 + L 1983/84 220-280 max. + R 1983/84, H 1985 P 1982/83/84 + L 1983/84 II 195-225 max. + R 1983/84 H 1985 P 1983/84 L 1983/84 III 195-225 red. reduced 0 R 1983/84 H 1985 P 1982/83/84 IV 150 0 0 0 H 1985 l) P = Passade, L = Lutterbek, R = Ratjendorf, H Heikendorf - 117 - Insect pests were counted weekly on 100 tillers per plot. Only the cereal aphids (Horn., Aphididae) were occurring in important numbers. Diseases of wheat were recorded weekly on 45 tillers per variable, which were taken to the lab. The degree of attack was recorded according to a scale 1-9, with 1 = free of attack and 9 = highest possible attack. Plots were harvested at the same time as the whole fields, leaving 1,5 m of the plots' margins apart. Grain yields were weighed at once, together with the determination of the water content of the grains. So yields per ha at 16 % of humidity could be calculated. Net outputs were calculated on the base of the grain yields, the actual wheat prices and the actual costs of fertilizing and of plant protection, including application costs. For testing the effects of nitrogen fertilizer and of chlormequat on cereal aphids, smaller plots were used (12 x 12 m), with 4 to 6 replicates. 3. Results 3.1 Nitrogen and cereal aphids Nitrogen fertilizers have been shown to be possibly one of the reasons for the increasing importance of the cereal aphids (HINZ & DAEBELER 1976, HANISCH 1980 and HANSEN 1986). But in the field, the stimulating effect of nitrogen on the population growth of aphids was not always clear (HANSEN 1986). In our experiments, increasing the amount of nitrogen was followed by a tendency of the aphids'increased population growth (Table 2). Table 2: The maximum (and relative) numbers of cereal aphids on small plots of winter wheat ("Kanzler") with different amounts of nitrogen fertilizers given. Heikendorf/Kiel (FRG), 1984 and 1985. In 1984, 90 % of the aphids were Sitobion avenae and 10 % Metopolophium dirhodum. In 1985, each of the 2 species represented 50 % of all aphids . 2 • /. not studied in 1984 maximum number of cereal aphids per 100 ears and flag-leaves (EC 75/85) year 150 kg/ha N 200 kg/ha N 250 kg/ha N 1984 3718 (100%) 4080 (110%) ./. 1985 4244 (100%) 4442 (105%) 4805 (113%) - 118 - 3.2 Chlormequat and cereal aphids The amount of nitrogen fertilizer given to wheat can be increased, if the stems have been stabilized with a growth regulator, most commonly chlormequat. This compound has been shown to decrease cereal aphid numbers (HINZ et al. 1976, FRITZSCHE & THIELE 1979). Four experiments, performed by us, 1983-1985, showed contradictory, not significant results (Table 3): in 2 trials, aphid numbers increased slightly after the application of CCC, in futher 2 trials they decreased. Table 3: The maximum attack by cereal aphids of winter wheat plots near Kiel, treated or not with chlormequat g a.i./ha maximum number of chlorme cereal aphids per year location variety kg/ha N quat (mid ear and flag leaf of April) (EC 75/85) With CCC Without 1983 Passade Disponent 195 920 1869 1704 (- 9%) Ratjendorf Monopol 225 1150 2453 3334 (- 36%) 1984 Heikendorf Kanzler 200 1150 875 1132 +230 (+ 30%) 1380 1111 1985 Heikendorf Kanzler 200 1150 1021 +230 (- 8%) 1380 So, the performance of the effects of N or CCC on cereal aphids is not stable. But the tendency seems prevailinq. that aphid numbers increase with the increasinq use of nitrogen fertilizers. - 119 - 3.3 Growinq intensity. wheat diseases. aphids. yields and net outputs The results of 7 experiments are summarized in Table 4. The application of funqicides proved to be not very effective: mildew (Erysiphe graminis) was controlled sufficiently in 4 of 7 trials, Septoria nodorum in 3 of 7 cases, eyespot (Pseudocercosporella herpotrichoides) in only 2 of 7 cases, and take-all (Gaeumannomyces graminis) - as expected - in no case. Cereal aphid control proved to be necessary and effective in 6 of 7 cases. No other insect pests occurred in important numbers. Grajn yields proved to be lowest in the variables of lowest intensity (III and IV). But the highest input (var. 1) gave in only 3 of 7 experiments the highest yield (not significant); in the other 4 cases the variable II gave the highest grain yields (partly significant). Concerning the net outputs (gross margins) the variables III and IV were lowest, and II highest (nit var. I). Since there did not exist any difference between var. I and II concerning pesticide input (Tab. 1) or the attack by pests and diseases (Tab. 4), the reason for the observed differences must be seen in the different amount of fertilizer given. With other words: The amount of N given to the plots of var. I was too high to be economic, it was uneconomic. This is important to note, since many farmers in Northern Germany still apply more than 220 kg/ha N (up to 300 kg/ha) to winter wheat. The problems arising from this are shown below. - 120 - Table 4: The maximum attack by fungal diseases and cereal aphids of winter wheat grown on large plots near Kiel (FRG), 1982-84, and the respective yields and gross margins. *** difference to var. I at p= 0,001, ** at p= 0,01, * at p= 0,05 1� 1 = no attack, 9 � maximum possible attack. 2) with insecticide ears and flag leaves maximum of attack grain net year field vari- Cereal yield out- at able diseases (1-9)1 ) aphids dt/ha put (see (Tab- mildew Sept. Eyespot Take- (sum) (16% (DM 1 a77 Tab- 1 e 1) ( f1 ag nod. (stem p. 100 H20) per 1 e 1) 1 eaf) (ear) base) (stem) e.+f. 3) ha) 1982 p I 1,3 4,0 4,1 3,9 120 98,0 3752 II 1, 1 4,2 5,1 4,0 170 95,7 3810 IV 1,3 5,0*** 5,8** 4,8 320 86,6** 3659 1983 p I 4,0 2,5 6,2 5,4 130 83,3 2954 II 4,3 2,7 5,8 5,1 120 93,9 3711* III 4,3 3,3 5,9 4,8 1350** 78,9 3112 IV 6,1*** 4,2** 6,7 5,1 2570*** 69,9** 2837 L I 3,7 3,1 7,1 5,2 140 88, 1 3197 II 3,9 3,2 6,6 5,0 110 85,9 3119 III 6,6* 3,6 7,0 5,5 1750*** 69,3* 2302* R I 4,0 3,2 7,1 5,9 80 58,6 1801 II 3,4 3,3 7,4 5,6 50 67,7* 2462* III 6,0*** 3,6 7,7 6, 1 4650*** 44,5** 1233* 1984 p I 1,7 3,9 3,1 3,8 30 91,8 3329 II 1, 9 3,2 3,2 3,8 50 94,7 3554 III 1,9 3,5 3,6 3,9 40 2) 91,5 2) 3424 IV 6,0*** 5,4** 6,4** 4,2 4380*** 55,3** 1233* llO L I 1,9 3,3 3,1 4,2 92,9 3092 II 2,0 3,4 2,6 4,0 90 92,0 3554 III 2,3 4,0 3,0 4,1 1420*** 80,5 2740* R I 2,1 3,5 3,6 4,0 750 87,7 2688 II 2,1 3,5 3,2 3,7 710 95,2 3096 III 2,3 4,1 4,0 4,0 5740*** 59,4** 1578* - 121 - 3.4 Nitrogen, Chlormeguat and the necessity of pesticide use Table 5 summarizes the results of an experiment carried out in 1985, which varied plant protection and nitrogen seperately. The data obtained reveal, that, if 250 kq/ha N are given, the maximum input of plant protection is inevitable. At a level of 200 kg/ha N the net output proved to be higher than at 250 kg/ha N in all plant protection intensities. At a level of 150 kq/ha N the net output was highest in the highest intensity, but the difference was not significant. At the lowest intensity of plant protection, best yields/qross margins were obtained at the lowest level of N. At the highest level of intensity, the differences (yield/net output) between N-levels were not significant. So, from the findings presented, it can be derived, that in regions, where wheat can be grown at a level of 300 kg/ha N, this level can be reduced to 150 kg/ha N without economic losses for farmers. Table 5: Cereal aphid attack, grain yield and net output of winter wheat ("Kanzler") grown at different intensities on small plots at Heikendorf/Kiel (FRG), 1985. *** significant difference to Var. at p= 0,001, ** at p= 0,01, * at p= 0,05 I II III herbicide, herbicide, herbicide kg/ha N chlormequat, chlormequat only fungicides &. fungicides & insecticide Cereal aphids 150 7 11* 12* per ear and 200 6 10* 11* flag leaf (max.) 250 6 10* 11* Grain yield 150 89,9 87,6 68,3** (dt/ha) 200 92,8 85,5 52,6** 250 89,9 79,9* 44,4*** Net output 150 3509 3448 2650* (DM/ha) 200 3629 3273 1757** 250 3408 2911* 1261** - 122 - 4. Discussion The studies presented here have shown again, that it is not only necessary to regard the actual grain yield, but also the net output. Furthermore it seems necessary, that every farmer, for the conditions prevailing in his farm, should try to reduce the input of N fertilizers, not regarding the grain yield, but the net output. Table 5 shows, that these experiments should lead to a reduction of N fertilization. With special view to the fact, that nitrates from agriculture are spoiling the quality of subsoil waters and have detrimental effects on coastal waters etc., the reduction of the use of N-fertilizers is inevitab1e from the environmental point of view. lt should be a good chance, if this goal could be achieved without monetary losses for the farmers or the society {when paying subsidies and/or environmental "repairing" costs). REFERENCES AL-NAJJAR, A., BASEDOW, TH. and SCHULZ, F.A. {1989): Die Auswirkungen abgestufter Produktionsintensitäten im Weizenanbau auf Schaderreger, Erträge und Wirtschaftlichkeit. I. Phytomedizinische Aspekte. - Z. Pflanzenkrankh. Pflanzenschutz 96, 561-584. BASEDOW, TH., SCHULZ, F.A. and AL-NAJJAR, A. {1990): Die Auswirkungen abgestufter Produktionsintensitäten im Weizenanbau auf Schaderreger, Erträge und Wirtschaftlichkeit. II. ökonomische Aspekte. - Z. Pflanzenkrankh. Pflanzenschutz 97 (in press). FRITZSCHE, R. and THIELE, S. {1979): Einfluß der CCC-Behandlung von Winterweizen auf die Blattlausvermehrung. - Nachrichtenbl. Pflanzenschutz DDR 33, 39. HANISCH, H.-CH. (1980): Untersuchungen zum Einfluß unterschiedlich hoher Stickstoffdüngung zu Weizen auf die Populationsentwicklung von Getreideblattläusen. - Z. Pflanzenkrankh. Pflanzenschutz 87, 546-556. HANSEN, W. (1986): Die Populationsdynamik von Blattläusen an Weizen in Abhängigkeit von der Qualität des Phloemsaftes bei unterschiedlicher N-Düngung. - Thesis Göttingen, 97 pp. HINZ, B. and DAEBELER, F. (1976): Der Einfluß der Stickstoffdüngung auf die Vermehrung der Großen Getreideblattlaus, Macrosiphum (Sitobion} avenae (F.) auf Winterweizen. - Wiss. Z. Wilh.-Pieck-Univ. Rostock, Math.-Nat. R. §, 653-655. HINZ, 8., DAEBELER, F. and GIESSMANN, H.-J. (1973): Untersuchungen zum Einfluß von Chlorcholinchlorid (CCC) auf die Entwicklung und Vermehrung der Getreideblattlaus Macrosiphum {Sitobion) avenae (F.) an Weizen. - Arch. Phytopathol. Pflanzenschutz�' 21-27. - 123 - INTEGRATED CONTROL OF RHOPALOSIPHUM PADI, AND THE ROLE OF EPIGEAL PREDATORS IN FINLAND J. HELENIUS University of Helsinki, Department of Agricultural and Forest Zoology, SF-00710 Helsinki, Finland Summary The monitoring of the exclusively holocyclic Rhopalosiphum padi in Finland is based on: 1) regional sampling for winter egg densities on the primary host Prunus padus, 2) suction trap catches of spring migrants and 3) sampling of shoots in fields of spring cereals. When the monitoring predicts peak population densities above the economic threshold, spraying with aphicides is recommended. The abundances of natural enemies are not taken into account in the regional monitor ing. In order to include the natural enemies in the inte grated control program, local populations should be monitor ed. The key questions in this are: what would be the impor tant species and how to make the sampling. Preliminary results from field experiments with oats in 1986 and 1988 are presented. Removal-trapping, pitfall trapping and predator manipulation methods were used. In 1986 Coccinella septempunctata was able to control R._ padi. In the outbreak season 1988, ingress-manipulation of epigeal predators resulted in a significant 53% reduction in peak aphid densities, in spite of heavy colonization pressure and high infestation levels of 40-120 aphids/tiller at the peak period. The importance of early season predation on R... padi is discussed. Emergence trapping of newly-emerged adults for studying recruitment rates of Bembidion spp. is suggested. 1 Introduction In Finland, populations of Rhopalosiphum padi (L.) have reached outbreak levels at 5-10 year intervals, and nine seasons in which severe damage occurred to spring cereals have been reported since 1928. Frequently, the aphid borne barley yellow dwarf virus has contributed to the crop losses (Kurppa, 1989b). Intensive research into R... padi was started about thirty years ago, and concerned distribution and damage, biolo gy, prediction and natural enemies. Until the 80's, the werk on natural enemies concentrated on the specialist predators, para sitoids and fungal diseases, and the role of generalist (epigeal) predators remained unknown. - 124 - 2 Research for developiag integrated control A survey of regional distribution and darnage was rnade during the outbreak season of 1959, when 50 000-70 000 ha was treated with 200-250 tn of parathion and DDT sprays and dusts. The average losses were estirnated to be 10%, while the effi ciency of the chernical control varied frorn prevention of total loss to yield irnprovernents of 10%. The low efficiency was because of the late application (Raatikainen & Tinnilä, 1961). The experience motivated studies on biology and darnage effects of !h_ padi and the associated virus (Markkula & Myllymäki, 1963; Markkula & Laurerna, 1964; Bremer, 1965). Rautapää (1968) developed an aphid-index, which is the integral of the aphid population growth curve, analogous e.g. to day-degree concept, and, in order to quantify the damage relationship, he cal culated regression lines of yield cornponents and %-loss against the index in oats. In 1974, Rautapää presented a method to predict the peak population density of !h_ padi, based on sarnpling for arrival of the first alate colonists and subsequent sarnpling for average density on the seedlings. A control scherne was presented, in which the spraying decision was rnade, when the rnonitoring predictea peak densities of 25 aphids per tiller. The calcula tions were based on the darnage relationship established in the earlier studies (Rautapää 1974, 1976, Rautapää & Uoti 1976). The prediction method was irnproved by introduction of winter egg counts: the rnortality of the eggs on the prirnary host is very low, and since the overwintering in exclusively holocy clic, egg counts early in winter can be used for predicting populations of spring rnigrants (Leather & Lehti, 1981; Leather, 1983). The present monitoring systern cornbines winter egg counts, suction trap samples, and incidence counts on seedlings (Kurppa, 1989a). Together with the studies aimed at designing a systern and establishrnent of thresholds for chemical control, alternative rnethods for aphid control have been looked for. Screening of cereal varieties for aphid resistance did not show rnuch promise (Markkula & Roukka 1972). The preference of !h_ padi towards cereals was dernonstrated, and at the same time, its relative polyphagy as compared to the other two mernbers in the guild of grass-feeding aphids, namely Sitobion aveane (Fabr.) and Meto polophiurn dirhodurn (Rautapää, 1970). Among the specific predators, the dorninatig groups are coccinellids, especially Coccinella septernpunctata L. and syr phid larvae. Aphidiids or Aphelinids frequently parasitize cereal aphids, and entornophthoraceous fungi are comrnon (Rauta pää, 1972; Clayhills & Markkula, 1974; Leather & Lehti, 1982; Rautapää, 1976; Papierok & Havukkala, 1986). The abundance of the specific predators and the rates of parasitism by parasit oids or fungal diseases are generally synchronized to the within-season developrnent of !h_ padi (Rautapää, 1976; Leather and Lehti, 1982; Helenius, 1990a). - 125 - 3 Role of epigeal generalist predators The major groups of epigeal generalist predators of R.,_ padi are ground beetles (Carabidae}, rove beetles (Staphylini dae}, and spiders (Araneae). The species lists from pitfall studies closely resemble those reported in the other countries in Northern Europe, with some exceptions; e.g. Agonum dorsale (Pont.) is rare in Finnish agricultural fields (Raatikainen & Huhta, 1968; Varis et al., 1984; Niemelä et al., 1987; Hele nius, in preparation). Experiments where predator densities were manipulated by barriers and ingress/egress trenches showed that the epigeal predators can reduce aphid infestation to the extent that yield is improved. Bembidion spp. (Carabidae) were indicated as the most important group, because of the highest activity-density during the colonization and establishment phase of R.,_ padi (Helenius, 1990b). Some preliminary results to supplement the earlier data are presented. The experiments were conducted at ° the Experimental Farm of the University of Helsinki (61 12 ' N}. 3.1 Material and methods The 1986 experiment consisted of 9 m2 plots of spring oats, replicated six times. Removal trapping for predators was started on the 2 9th of May at the 1- 2 leaf stage (GS 11-12), on the same date the first alate colonists of R.,_ padi were obser ved. The method used has been described by sunderland et al. (1987), except that vacuum netting was not made because of the soil was too loose, and there was only one pitfall trap of 80 mm in diameter inside the isolator, 10 cm from the wall in a shallow pit mimicking the strategy of ant lion. The 30 cm high isolators, 57 cm in diameter, were made from former paint drums and were driven 2 0 cm deep into the soil. Isolators were kept for 2 8 days, starting with three in every second plot and then adding three more after 14 days in the other plots. The six isolators were then operated so that each of the four over lapping trapping periods was replicated in three of the plots. One pitfall trap was placed in ;he middle of each plot. Thus, altogether 12 circl�s of 0.25 m was sampled, the total area covered being 3.0 m.Pitfalls were emptied once every 3-4 days. Population densities of R. padi were monitored by sam pling tillers. The 1988 experiment aimed at estimating the effect of predator exclusion on the yield of oats in monocrops and in mixed stands with faba bean. The aspect of mixed cropping and plant competition will not be treated here. Plots of 3m x 6m were used, and the treatments were arranged in sub-plots of 1.25m x 2m. These were sraying with aphicide (dimethoate), ingress-only trench, control, and egress-only trench (for the method in arranging the manipulations, see Helenius, 1990b). There were four replications. The aphid densities were esti mated by inspecting tillers in situ. The effect of trenches was not controlled by pitfall trapping of predators as in the earlier experiments in which these always operated well (Hele nius, 1990b). Grain yields of oats were determined. - 126 - 3.2 Results The removal trapping by isolators yielded very few cara bids of predatory importance. The burrowing species Clivina fossor was the most abundant carabid in the catch: the average catch from the isolators was 0.8/trap-day, while the catch from the control pitfalls was 0.9/trap-day. There was a peak in late July in isolators as well as in control pitfalls. The ground search yielded altogether 11 Q_,_ fossor. Trechus secalis ranked as the second largest catch from the isolators. All the other carabids were very few in the removal traps, and none was found , by ground searching (Table 1). Q_,_ septempuctata �as exceptionally abundant early in the season. The peak coccinellid activity was during the 26th of 1 June until 3rd of July, when the catch of larvae was 26.6±3.0(S.E.)/pitfall-day in the control pitfalls. The ground search o� the 26th of June gave an estimated density of 100.0 larvae/m . The abundance of coccinellid larvae in the isolators during the second period was because of the difficulties in preventing the very numerous small larvae from entering the trap when remcving the sealing net while emptying the pitfall (Table 1). The development of the population of R.. padi indicated an outbreak, but on the 25th of June a sudden decline at GS 43 (boots just visibly swollen) was observed: 11/6 16/6 18/6 23/6 25/6 30/6 R.. padi mean no. per tiller 0.6 3.5 4.1 6.3 3.0 0.3 The decline was not associated with the normal symptoms of a degenerating population such as the abundance of overcast skins, infected or parasitized aphids or dvelopment of alate morphs. Numbers of syrphid larvae were also negligible. The aphid populations did not recover in the experiment nor in the surrounding cereal fields. In 1988, there was a mass invasion of long distance migrants of R.. padi to cereal fields at GS 10-12 (one to two leaves), resulting in an extreme colonization rate of 30% of seedlings infested in the experiment. After a week, the excep tionally large native migrant populations moved to grasses, contributing to the extended colonization period of two weeks (see also Kurppa, 1989b). The populations reached peak densi ties 2-3 weeks earlier than normally in mid-June, at GS 4-5 (late booting, P.arly panicle emergence). Measured by DD accumulation, the early season was very warm which explains the rapid development of the cereals. The resulting peak densities of aphids in the experiment were all above the economic damage threshold of 20-25/tiller. In the sprayed plots there still were aphid colonies in spite of three applications of dimethoate. The ingress-only treatment reduced the peak densities by 53% (LSD-test for ln-transformed values, p<0.05) in comparison to open controls. The average increase of 27% achieved by the predator exclusion treatment was not significant (F-test, df=2,12). The aphicide treatment resulted in a 75% increase in oats yield when compared to the control (LSD=950 kg/ha, p<0.01). In the ingress-only treatment the average yield was 33% higher than in the control, but the difference was not significant (F-test, df=3,18) (Table 2). - 127 - Table 1. Catches of most abundant species of Carabidae and Coccinella septempunctata from pitfall-traps, and catches from ground search. (There were 84 trap-days/period and 0.75 m2 was searched per period.) Period 29/5-26/6 12/6-10/7 26/6-24/7 10/7-7/8 A. Control pitfalls (number/trap-day) Bembidion spp., all 0.2 0.1 0.2 0.2 - 1h_ guttula (Fabr.) 0.1 o.o 0.1 0.1 Clivina fossor (L.) 1.1 0.3 0.7 1. 4 Harpalus rufipes (Deg.) 0.3 0.3 0.4 0.4 Pterostichus melanarius (Ill.) 0.2 0.3 0.9 1.1 Trechus secalis (Payk.) 0.2 0.3 0.7 0.8 g.,_ septempunctata L., ad. 0.8 0.6 1.3 1.1 Coccinellidae, larvae 1.1 6.1 8.1 0.0 B. Pitfalls inside the �solators [no./trap-day (no./m )] 1h_ guttula o.o (1) g.,_ fossor 0.4 ( 51) 0.5 (53) 0.4 (51) 1.8(196) .E..... melanarius o.o (1) o.o (1) � secalis 0.0 (5) o.o (3) o.o (1) o.o (7) g.,_ septempunctata, ad. o.o (1) Coccinellidae, larvae 0.0 (7) 0.6 (64) 0.2 (21) c. Ground search (no./m2) g.,_ fossor 12.0 1. 3 1.3 g.,_ septempunctata, ad. 1. 3 17.3 Coccinellidae, larvae 100.0 5.3 Table 2. Peak population density of R..,_ padi and grain yield of oats in 1988 predator manipulation experiment. (Standard errors are given in brackets. Means within column followed by same letter are not significantly different.) R. padi Oats yield number/tiller kg/ha Egress-only 114.6 (10.3) a 3 063.9 (576.2) a Control 90.3 (14.3) a 2 695.4 (341. 3) a Ingress-only 41.8 (9.9) b 3 589.0 (476.1) a Aphicide (some colonies) 4 745.4 (493.6) b - 128 - 4 Discussion The experience in 1986 showed how .Q_,_ septempunctata alone can control !L_ padi, provided that the abundance and activity are high enough during the establishment phase of the prey population. At the moment, there is no method to predict abun dance of coccinellids. The weather plays an important role in determining the activity of coccinellids during the critical colonization and establishment phases of R.,_ padi. Predation by coccinellids is facilitated by warm and dry weather. In these circumstances, action threshold of aphicide spraying could be raised. Relative to the pitfall catches, the catches of carabids in the removal traps were low. The number of traps used was clearly too small for accurate estimation of absolute popula tion densities of carabids. Another problem was that operating the traps for four weeks may have allowed newly-emerged adults to be caught. The 1988 experiment indicated that epigeal predation can significantly reduce peak aphid densities also in years of heavy colonization. This may have been facilitated in the season 1988 by the very early arrival of the colonists, which became exposed to predation by Bembidion spp. when these were most numerous and abundant. However, the aphid populations exceeded the economic damage threshold also in plots where predation was enhanced by ingress-only treatment, and no yield improvement was achieved, contrary to the results at moderate infestation levels (Helenius, 1990b). BYDV-infestation was an important component of the aphid damage during the season (Kurppa, 1989b, Kurppa et al., 1989). In order to prevent the spread of the virus the aphid popula tions should be controlled early. This requirement creates problems in relying on natural enemies: a monitoring scheme should reliably predict the impact of predation before the aphicide should be sprayed, within two weeks from the arrival of the first colonists. The present prediction system (Kurppa, 1989a) is reliable and, according to a similar survey as performed in 1959, it resulted in a much better protection of the crops during the outbreak of 1988 than was the case during the outbreak of 1959 (Kurppa, 1989b). However, the scheme relies entirely on the use of aphicides: the next challenge would be to include the coc cinellids and general epigeal predators into the integrated control of R. padi. Cultural methods should be developed that enhance the epigeal predators early in the season. When comparing different cultural practices it would be important not only to estimate population densities or mortality rates of the overwintered adults, but also to obtain data on their reproductive success. For this purpose, emergence traps could be used (Fig.). A preliminary result of emergence trapping for recruitment rate of Bembidion spp. in a spring barley field was 15-20 newly emerged specimens per square meter, the development time being ca. 400 day-degrees (>5 ° C) (Helenius, Holopainen and Tolonen, in preparation). - 129 - Trap-area is 0.24m 2 vertical barriers enclosing a 0.5m x 0.5m square pitfall traps of � 10cm in each corner topsoil ca. 5cm Figure. Illustration of an emergence trap for trapping newly emerged carabids in a cereal field. For winged species a seal ing net would be required. The trap may not be suitable for burrowing species. Acknowledqements I wish to thank the members of the Nordic Research Group for collaboration, and Mr Robert Harper for linguistic revision of the manuscript. The study was funded by the National Research Council for Agriculture and Forestry. References 1. BREMER, K. (1965). Characteristics of the barley yellow dwarf virus in Finland. Ann. Agric. Fenn. 4: 105-120. 2. CLAYHILLS, T. and MARKKULA, M. (1974). The abundance of coccinellids on cultivated plants. Ann. Ent. Fenn. 40: 49- 55. 3. HELENIUS, J. (1990a). Incidence of specialist natural ene mies of Rhopalosiphum padi (L.) (Hom., Aphididae) on oats in monocrops and mixed intercrops with faba bean. J. Appl. Ent. 109: 136-143. 4. HELENIUS, J. (1990b). Effect of epigeal predators on infes tation by the aphid Rhopalosiphum padi and on grain yield of oats in monocrops and mixed intercrops. Ent. Exp. et Appl. In press. 5. KURPPA, A., KURPPA, S. and HASSI, A. (1989). Importance of perennial grasses, and winter cereals as hosts of barley yellow dwarf virus (BYDV) related to fluctuations of vector aphid population. Ann. Agric. Fenn. 28: 309-315. 6. KURPPA, s. (1989a). Predicting outbreaks of Rhopalosiphum padi in Finland. Ann. Agric. Fenn. 28: 333-347. 7. KURPPA, s. (1989b). Damage and control of Rhopalosiphum padi in Finland during the outbreak of 1988. Ann. Agric. Fenn. 28: 349-370. - 130 - 8. LEATHER, S.R. (1983). Forecasting aphid outbreaks using winter egg counts: An assessment of its feasibility and an example of its application in Finland. z. ang. Ent. 96: 282-287. 9. LEATHER, S.R. and LEHTI, J.P. (1981). Abundance and survi val of eggs of the bird cherry-oat aphid, RhopalosiphU:m padi in southern Finland. Ann. Agric. Fenn. 47: 125-130. 10. LEATHER, S.R. and LEHTI, J.P. (1982). Field studies on the factors affecting the population dynamics of the bird cherry-oat aphid, Rhopalosiphum padi (L.) in Finland. Ann. Agric. Fenn. 21: 20-31. 11. MARKKULA, M. and LAUREMA, s. (1964). Changes in the concen 1 tration of free amino acids in plants induced by virus diseases and the reproduction of aphids. Ann. Agric. Fenn. 3: 265-271. 12. MARKKULA, M. and MYLLYMÄKI, S. (1963). Biological studies on cereal aphids, Rhopalosiphum padi (L.), Macrosiphum avenae (F.), and Acyrthosiphum dirhodum (Wlk) (Hom., Aphi didae). Ann. Agric. Fenn. 2: 33-43. 13. MARKKULA. M. and ROUKKA, K. (1972). Resistance of cereals to the aphids Rhopalosiphum padi (L.) and Macrosiphum ave � (F.) and fecundity of these aphids on Graminae, Cype . raceae and Juncaceae. Ann. Agric. Fenn. 11: 417-423. 14. NIEMELÄ, J., HAILA, Y. and HALME, E. (1987). Carabid assem blages in southern Finland, a forest-field comparison. Acta Phytopath. Ent. Hung. 22: 417-424. 15. PAPIEROK, B. and HAVUKKALA, I. (1986). Entomophthoraceous fungi parasitizing cereal aphids in Finland. Ann. Ent. Fenn. 52: 36-38. 16. RAATIKAINEN, M. and HUHTA, V. (1968). On the spider fauna of Finnish oat fields. Ann. Zool. Fenn. 5: 254-261. 17. RAATIKAINEN, M. and TINNILÄ, A. (1961). ·occurrence and control of aphids causing damage to cereals in Finland in 1959. Publ. Finn. State Agric. Res. Board 183. 27 p. 18. RAUTAPÄÄ, J. (1968). Changes in the yield and protein quantity of oat caused by Rhopalosiphurn padi (L.) (Hom., Aphididae). Ann. Agric. Fenn. 7: 95-104. 19. RAUTAPÄÄ, J. (J.970). Preference of cereal aphids for va rious cereal varieties and species cf Grarninae, Juncaceae, and Cyperaceae. Ann. Agric. Fenn. 9: 267-277. 20. RAUTAPÄÄ, J. (1972). The importance of Coccinella septem punctata L. (Col., Coccinellidae) in controlling cereal aphids and the effect of aphids on the yield and quality of barley. Ann. Agrlc. Fenn. 11: 424-436. 21. RAUTAPÄÄ, J. (1974). Viljan kirvat - torjunta ja runsauden ennustarninen. Kasvinsuojelulehti 7: 35-42. 22. RAUTAPÄÄ, J. (1976). Population dynarnics of cereal aphids and method of predicting population trends. Ann. Agric. Fenn. 15: 272-293. 23. RAUTAPÄÄ, J. and UOTI, J. (1976). Control of Rhopalosiphurn padi (L.) (Horn., Aphididae) on cereals. Ann. Agric. Fenn. 15: 101-110. 24. SUNDERLAND, K.D., HAWKES, C., STEVENSON, J.H., McBRIDE, T., SMART, L.E., SOPP, P.I., POWELL, w., CHAMBERS, R.J. and CARTER, O.C.R. (1987). Accurate estimation oof invertebrate density in cereals... Bull. SROP/WPRS Bull. 1987/X/1: 71-81. 25. VARIS, A.-L., HOLOPAINEN, J.K. and KOPONEN, M. (1984). Abundance and seasonal occurrence of adult Carabidae (Co leoptera) in cabbage, sugar beet and timothy fields in southern Finland. z. ang. Ent. 98: 62-73. - 131 - Effects of some insecticides on aphids and beneficial ar thropods in winter wheat U. Heimbach Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für Pflanzenschutz in Ackerbau und Grünland sunmary The results of fieldtrials with some aphicides in win ter wheat are presented. In 1988 pirimicarb turned out to be the most effective aphicide; fenvalerate and pa rathion had similar effects and endosulfan was less ef fective. In 1989 lambda-cyhalothrin and again pirimi carb were very effective. The effectiveness of the three other insecticides was comparable to that of 1988. Apart from effects on aphids the mortafity of benefi cial arthropods was observed. The number of dead in sects counted after the application was nearly the same in the untreated or pirimicarb treated plots. But _more dead insects were found in the fenvalerate, endosulfan and even more in the parathion treated plots. In 1989 in the lambda-cyhalothrin treated plot were about 10 times as much dead insects as in the parathion plot. The number of spiders caught with pit fall traps and ground photo-eclectors was reduced in the endosulfan, fenvalerate and especially in the lambda-cyhalothrin treated plots. Altogether pirimicarb turned out to be very effective on aphids but ineffective on beneficials. Lambda-cyha lothrin had the most marked effects on aphids and bene ficial arthropods. 1.1 Introduction The aim of the IOBC working groups "Integrated control in cereal crops" and 'Pesticides and beneficial organisms" is to reduce the number of applications and the amount of pesticides used and to find out selective pesticides. Therefore a trial programme was started with some aphicides in winter wheat in West Germany in that we looked for both, effectiveness on the aphids and on some beneficial arthro-· pods. - 132 - 1.2 Material and Methods Field experiments Field studies were performed in 1988 and 1989 near Braunschu>eig in winter wheat (plot size: 1 ha) conventio nally treated with fertilizers and pesticides. The aphici des ( table 1.) were sprayed wi th a conmon field spraying machine ( 300 1 water per ha) . To count the aphids 50 ears and 50 flag leafs per plot were cut off and all insect were extracted by a simplified Kempson-extractor (KEMPSON et al. 1963). Table 1. : Aphicides used in the trials in the different plots. The efficacy of pirimicarb was very high along with quick killing of the aphids. Parathion and fenvalerate were a little bit less effective and endosulfan even less. But alreact�, some days after the application the population density in the untreated plot decreased. In 1989 the application was at GS 61-65 (12 June 89). At that time about 8 aphids were found per ear and flag leaf (fig. 2.). Pirimicarb and lambda-cyhalothrin were very effective. The effectiveness of the other three insectioäes was quite com parable to that of 1988. But in 1989 the population density of the aphids increased some days after the application. In both years about 90 % of the aphids were Sitobion avenae. The number of thysanopteres (about 8 per ear and flag leaf were extracted in 1989) was reduced slightly in both years by the applicaton of parathion. In 1989 lambda-cyhalothrin reduced them by about 75 %. The other insecticides did not effect the thysanopteres. But it has to be mentioned, that the extraction-method gave less than 100 % of the number of thysanopteres. Beneficial arthropods In 1988 we collected dead insects on successive days in the tram lines (table 2.). Parathion killed most of the collected beneficial arthropods. Even 3 days after the application we found some dead ones. In 1989 (table 3.) the Table 2. : Collecting of dead animals in trarn lines (600/400 m) after the application treatrcent 04-07-1988 number of dead predatory number of dead Diptera Coleoptera and Araneae and Hymenoptera a.i / ha 5-07 6-07 7-07 total 5-07 · 6-07 7-07 total untreated 3 0 0 3 0 0 0 0 pirimicarb 100 g 11 0 1 12 25 4 2 31 fenvalerate 30 g 11 0 0 11 8 2 0 10 endosulfan 213 g 30 8 0 38 42 11 0 53 parathion 105 g 63 6 15 84 62 8 14 84 number of dead insects counted after the application was nearly the same in the untreated and the pirimicarb treated plots. But as in 1988 more dead insects were found in the fenvalerate, endosulfan or parathion treated plots. In 1989 in the lambda-cyhalothcin treated plot were about 10 times as many dead insects as in the parathion treated plot. Even. 10 days after the application beneficials were still dying - l34 - 1989 CO i4 ...... J OI application ...... CO 12 june 1989 u.. i2 "'CC: CO c.. iO CO c.. Cl.) 8 C...... c: 6 C. 4 ..... 2 0 8 june 12 june 15 june 19 june 26 june 3 july 10 july -+-� 26..--..,,-,------1988 ------...J ap�lication OI 24 4. JUly 1988 \ � -1 • ------11ntreated ..____ _ - -- p1r11,11carb ---e,-ci � :i endosulfan· ------� i parathionr · · · · · t'.B \ \ fenvalerate ··················-«> c.. i6 \ \ · Cl.) \ la1Eda-cyh. · · · ·· -<;>, c. ' i4 ' tl'j "'C. \ \ ... i2a.. \ \ -§. ····· ' < iO \ ·····. . \ .....o . \ B \-.\.\ ... ,\., ·· .... � 6 \ ···· ... , ...... · 4 . \-�- ···... ',,, . 2 · - · ·· ··· ··· ···:···:···:�-. O-t------.----.------. -. &: -: :-: -- �,.,;;,..,;&------,,.;-----. . --·.::::1f- l july 5 july 7 july 11--, july .,.;.,.;,..,,:,.., . . 18 july fig. 1. Nurnber of aphids per ear and fläg leaf at different dates before and after the application of insecticides in wheat - 135 - in this plot, whereas at the same time the population den si ty of aphids already increased. In 1988 40 % of the collected dead predators were carabids and 45 % staphyli nids. In 1989 10 % were carabids, 20 % coccinellids and 63 % staphylinids, most of them Tachvporus spec. Due to the cannibalism of other predators like cara bids, mice and birds only an unknou,n percentage of the arthropods hit by an application will be found. Also many small predators and soft-skinned arthropods like spiders cannot be found if they are hit by a pesticide. Sampling of dead insects · is a quite rough method, but at least the effects of · different treatments can be evaluated if the plot size is sufficient and the density of the predators in the plots is comparable. Table 3.: Collecting of dead animals in tram lines (400 m) after the application treabnent 12-06-1989 nurnber of dead predatory Coleoptera and Araneae f0tmd a.i / ha 13-06 14-06 15-06 19-06 20-06 22-06 total untreated 0 2 0 0 0 1 3 pirimicarb 100 g 2 0 2 0 4 fenvalerate 30 g 8 10 9 0 27 endosulfan 213 g 5 3 2 (10) 11 parathion 105 g 17 2 1 0 31 lambda- 10 g 97 70 92 14 15 12 300 cyhalothrin nurnber of dead Diptera andHyrrenoptera found a.i / ha 13-06 14-06 15-06 19-06 20-06 22-06 total untreated 0 0 0 0 0 1 1 pirimicarb 100 g 1 0 0 0 1 fenvalerate 30 g 5 5 0 0 10 endosulfan 213 g 2 0 0 (2) parathion 105 g 1 0 1 1 0 3 lambda- 10 g 29 28 23 0 4 6 90 cyhalothrin - 136 - fig. 2. Number of spiders caught with pit fall traps (10 per plot 1988, 5 per plot 1989) at different dates ( 1988: 1 = 29 jure - 4 july, 2 = 6 - 11 july; 1989: 1 = 9 - 12 jure, 2 = 13 - 19 jure, 3 = 19 - 26 jt.r.e) - 137 - The results of the laboratory test (table 4.) show, though laboratory tests like this are a kind of worst case test, that only parathion had effects an the mortality of Poecilus cupreus. Endosulfan, fenvalerate and pirimicarb had not even effects on the reproductivity of this carabid beetle. The influence of parathion on the reproductivity is caused by the lack of males after the application. Table 4.: M:>rtality and reproduction of Poecilus cupreus in a laboratory test treatroent 4-07-1988, (5 replicates, 5 beetles each) % rrortality hatched of adults mnnber time of develop. beetles per a.i / ha 29-08 24-11 of eggs larva - adult 100 eggs untreated 4 4 1183 42,5 days 39 pirimicarb 100 g 4 16 1445 45,3" 35 fenvalerate 30 g 4 4 1961 44,7" 40 endosu lfan 213 g 4 32 1582 42,8" 49 parathion 105 g 84 84 41 O The number of Araneae ( fig. 2.) caught in pit fall traps after the application was influenced particularly by lambda-cyhalothrin and fenvalerate treatment (fig. 3.). But also parathion and endosulfan seem to have negative ef- . fects. The acti vity of spiders an the soil surface was en hanced by the pirimicarb application which might be due to the high numbers of dying aphids an the soil surface and the lack of aphids as prey within the crop. But the amount of insects caught in pit fall traps is influenced by many factors so that the results are difficult to interpret and often not sufficient (BASEDOW et al. 1987). In 1989 there were not enough carabids and other predators except spiders in the pit fall traps to allow any interpretation. In 1988 changing weather condi tions before and after the applica tion led to very different numbers of predators even in the untreated plot; to give an example: 3,9 Pterostichus spec. per day and trap to only 1,1 after the application. Ground photo-eclectors catch all insects within the eclector, that are attracted by light. Fig. 4. gives the number of Araneae caught by eclectors. Fenvalerat and lambda-cyhalothrin shou., distinct effects on spiders. But a more thorough examination of the effects of parathion and especially endosulfan an spiders ought to be done. The eva luation of the trial programme is not yet completed. There were quite a lot of Staphylinidae in the photo-eclectors that may indicate some additionally effects. - 138 - -40 -20 t6() lambda endosulfan. parathicn fenvalerate •100 pirimicarb cyhalothr in B6 B9 BB 89 BB 89 BB B9 BB 89 year fig. 3. Effectiveness (HENDERSON & TILTON 1955) of some insecticides an spiders caught with pit fall traps ( 1968: jt.ne - 4 july ard � _ 6:.. 11,july, appl. 4 july; 1989: 9 - 16 jLJ1e ard 13 - 26 Jt.ne, appl. 12 JLJ1e) Altogether pirimicarb, with an applicat.ion rate that uras .reduced from 150 g a. i /ha (official ly recommended rate in West Germany) to 100 g a.i/ha, turned out to be very effective on aphids but ineffective on beneficials. Lambda cyhalothrin had the most marked effects on aphids and bene ficial arthropods. The results of the trials show that from the entomological point of view pirimicarb should be used in integrated pest management in winter wheat. References Basedow, T., Beckmann, C., and Runge, I. (1987). Problema tik von Freilandversuchen zur Prüfung der Wirkung von Pflanzenschutzmitteln auf epigäische Raubarthropoden im Ackerbau. Z. Pflanzenkh.Pflschutz. 94, 260-275 HEIMBACH, U. (1988). Nebenwirkungen einiger Fungizide auf Insekten. Nachrichtenblatt des Deutschen Pflanzen schutzdienstes 40 (12), 180-183 HEIMBACH, U. (1989). Massenzucht von Poecilus cupreus (Col., Carabidae). Verhandlungen der Gesellschaft für Okologie Osnabrück 1989, Bd. XIX/I, 228-229 Henderson, C.F. and Tilton, E.W. (1955). Test with acarici des against the brourn wheat mite. Journal of Econ. Entomol. 48, 157-161 Kempson, D., Lloyd, M. and Ghelardi, R. (1963). A new ex tractor for woodland litter. Pedobiologia 3, 1-21 - 139 - 1989 ARANEAE/m' application 12 june 250 l = 5 - 13 june 2 = 13 - 20 june 3 = 20 - 28 june 200 4 = 28 june - 4 july 5 = 4 - 10 juiy ISO 100 so 1 2 3 4 5 1 2 3 4 5 2 3 4 5 2 3 4 5 12 345 2345 fenvalerate lambda- untreated pirimicarb endosul fan· parathion cyhalothr in ARANEAE/m' 1988 45 application 4 july l = 1 - 4 july 40 2 = 5 - 8 july 35 30 25 20 15 10 5 2 2 2 untreated pirimicarb endosulfan fenvalerate fig. 4. Number of spiders caught wi.th ground photo-eclectors (1m2) at different dates - 140 - ACTIVITY AND POPULATION DENSITY OF EPIGEAL ARTHROPODS IN FIELDS OF WINTERWHEAT M.LÜBKE(*) (*) Martin-Luther-Universität Halle-Wittenberg, SektionPflanzenproduktion, Lehrstuhl Phytopathologie und Pflanzenschutz, Ludwig-Wucherer-Straße 2, 4020Halle (S). F.R.G. SUMIV..ARY Experiments for estimating activity density of epigeal arthropods were carried out from April to August of the years 1986 to 1989 near Halle/S. (FRG) with pitfall traps. Alltogether 8 formalinfilled pitfall traps let into the soil so that 4 traps were standing in 25 m and 100 m distance from field edge. Pitfall traps were emptied weekly. Experiments should give results about proportions of epigeal arthropods, their activity density and dominance structure. RESULTS * Activity density Spiders (Araneae), ground beetles (Carabidae) and staphylinid beetles (Staphylinidae) mostly characterized as carnivorous although within this taxa are phytophagous (Carabidae) and saprophagous or omnivorous (Staphylinidae) living species. This fact was not considered. Proportion of spiders amounts to 53 to 58 per cent, those of ground beetles 10 to 17 per cent in the years 1986 to 1989 (Table 1). The proportion of Staphylinid beetles was between 29 and 35 per cent. There were no essential differences between the separate years. Activity density of spiders always reached its maximum mid to end July. The highest activity density was registered in 1988 with 20 individuals per day and trap. Most of spiders belong to the Linyphiidae, especially Erigoninae and Linyphiinae. Staphylinid beetles catches reached a - 141 - maximum of 5 individuals per day and trap. There were no large differences between the separate years. Catches in spring were higher as in the summer months. Tue high numbers of staphylinids in spring were due to the msot frequent species Tachyporus hypnorum (L.). Tue most interestinggroup of epigeal arthropods arethe ground beetles. Tue maximum catch was 3 individuals per day and trap. Tue activity density in the separate years was relative1 :, constant. Most beetles were catched when the weather was wet and warm. Furthermore the dominance of the different species in wheat fields was exarnined. Poecilus cupreus (L.) always renders as eudominant species. Platynus dorsalis (Pont.), also was an eudominant species, with exception of 1987. Further eudominant and dominant species were Bembidion lampros (Herbst), Bembidion quadrimaculatum (L.) and Pterostichus melanarius (111.). Diversity index (Hs) and eveness (E) of the ground beetle communities were calculated (table 2). Diversity of groundbeetles in 1988 was the highest. Tue eveness refers to regular share of the species. In 1988, 5 species reached a proportion of over 10 per cent of the whole catch. However differences of diversity and eveness between the separate years were low. Moreover a comparison of the catches was carried out regarding species identity (Jaccard's index) and dominance identity (Renkonen's coefficient) between the separate wheat fields (table 3). Mostly there were between the years 22, between 1986 and 1989, 24 common species and only 11 not common species. Tue Jaccard's index showed this fact. Tue relative frequencies of the species corresponding to 84 per cent between 1986 and 1987. Similarity of catches in 1988 and 1989 only correspondingto 56 per cent. In relation to 1988 all years showed not so high correspondence. As reason come into question the species Poecilus cupreus (L.) which amounted to an activity dominance of 32 per cent in 1986, 36 per cent in 1987, 38 per cent in 1989 and only 11 per cent in 1988. This species also has had a low activity density in 1988. * Popuiation density Investigations of population density of epigeal arthropods were first of all applied to registration of ground beetles. In this purpose square-meter-method, capture-recapture method and wet extraction were used. These methods should be compared with regard to assertion about population density of ground beetles. As fare as it was possible by use of this methods to catch spiders and staphylinid beetles, an estimation of population density was done. Above methods require relative much time for accomplishment. Therefore mostly only a low number of repetitions were possible. - 142 - Table 1 : Proportions(in per cent) of epigeal arthropodsin winter wheat. 1986 1987 1988 1989 Araneae 58 53 53 56 Carabidae 13 17 12 10 Staphy linidae 29 30 35 34 Table 2 : Diversity index (H5) and Eveness (E) of groundbeetle communities in winter wheat 1986 1987 1988 1989 Species quantity 29 28 32 30 Diversity 2,28 2,20 2,46 2,18 Eveness 0,68 0,66 0,71 0,64 Table 3 : Species identify (Jaccard's index cj) and dominance identify (Renkonen's coefficient : ID) of groundbeetle communities in winter wheat. 1987 1988 1989 cj/ID cj/ID cj/ID 1986 1,69/83,51 1,29/67,12 2,18n6,87 1987 1,64/66,26 1,51no,62 1988 1,22/55,90 - 143 Square-meter-method Experiments were carried out in the years 1987 and 1988 at 25 m and 100 m distance from field edge. Quadrats of one meter side lenght consisted of plastic material pressed into soil. Hang over plants were cut to prevent an escape of animals. Each quadrat preserved three formalinfilled pitfall traps. Pitfall trapswere emptied firsttime 48 hours after the beginning of the experiment, then weekly after sinking into soil. Catches of differentground beetles and of the three groups of epigeal arthropods are represented in table 4. There are discemible tendencies to results of activity density. A comparision of activity and population density of the most important ground beetle Poecilus cupreus (L.) was carried out. At May and June of 1987 three individuals par m2 were established. Activity density at this time was also high. The low catcheswith pitfalltraps in 1988 face adequate population densities. Capture-recapture-method Plots of 4 m2 size were established fromplastic material. Four dry pitfall traps were sinked in this plots. Traps were emptied at intervals of a few days. Catched beetles were markedwith nitro colour and after then left back into the plots. A populationdensity of two individuals per 2 m of Poecilus cupreus (L.) was ascertained by this method. At June of 1988 the population density of this beetle was 0,5 individuals per m2 what corresponds with results of the square meter-method. Assertions about spiders and staphylinid beetles were not possible by this method. Wet extraction Investigationswith wet extraction (BRENOE, 1987) carried out only at May till July in 1988. 2 Quadrats of 1 m size made of plastic material were sinked into soil. After that 120 1 water were poured in the separate plots which were observed for nearly half an hour. Only small beetles especially Trechus quadristriatus (Schrank) were catched. By pitfall traps at this time only 0,02 individuals per day and trap were sampled. By use of this method also many staphylinid beetles especially Tachyporus hypnorum (L.) werecatched. Definitive methods should be estimated with regard to their practical application. Investigations for activity density are easy to carry out. There are scarcely subjective mistakes. All groups of epigeal arthropods may be catched, estimating population density is only possible by square-meter-method,partly also with wet extraction. Tue capture-recapture method is suitable for population density investigation of ground beetles, but it is more expensive. The use of the methods should be choosen adequate to the aim. - 144 - Table 4 Results of square-meter-method for estimating population density of epigeal arthropods. 13.5.87- 26.5.87- 18.5.88- 1.6.88- 22.6.88- 26.5.87 18.6.87 1.6.88 22.6.88 1.88.88 P. cupreus 2,50 3,25 0,25 0,50 0 P. dorsalis 0,75 1,00 1,00 0,75 0 P. melanarius 0,25 0,50 0,25 0,50 0 T. 4-striatus 0 0,50 0 5,50 2,50 other species 1,00 3,00 5,75 4,25 5,00 Carabidae 4,50 8,25 7,25 11,50 7,50 Staphylinidae 83,00 51,25 59,75 131,00 114,00 Araneae 12,25 6,50 3,25 21,75 65,50 Results of experiments for activity density were used for predator-prey-relations. This is especially interestingbecause the active animalsare catched. As well this methodare applied for investigations of side effects of pesticides against beneficial arthropods. Those experiments can be completed by square-meter-method or wet extraction. Wet extraction probably renders catches of beetles with high population density and low activity density like the species Trechusquadristriatus (Schrank). REFERENCE BRENOE, J. 1987. Wet extraction - a method for estimating populations of Bembidion Iampros (Herbst) (Coleoptera, Carabidae). J. appl. Ent. 103, 124-127. - 145 - TRAVAUX REALISES EN FRANCE, A L'INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE, SUR LA PYRALE DU MAIS, 0-0tlu.ruit nub..ii.aLL6 Hbn. (Lep. Pyralidae) N. HAWLITZKY Station de Zoologie CRA de Versailles 78026 VERSAILLES CEDEX En France, un des ravageurs du mais, 0-0tlu.ruit nub..ii.aLL6 Hbn. (Lep. Pyralidae) est tres etudie : insecte d'interet 3gronomique, il peut, par les degäts que produisent les stades larvaires, entrainer des diminutions de rendement notables allant jusq'a 20 quintaux/ha, ce qui represente 1/4 a 1/5 des rendements obtenus. Ce ravageur sevit, avec un nombre variable de generations selon les regions, du SUD-EST et du SUD-QUEST (2 generations), au BASSIN PARISIEN (1 a 1 ,5 generations) et a 1 'EST de la France (1 generation, ALSACE). Depuis environ 2 ans, il commence a envahir le NORD-QUEST. Campte tenu de son importance economique, cette pyrale est 1 'objet d'une concentration de travaux de recherches tant fondamentaux que final ises. Plusieurs laboratoires de 1 'INRA, (en collaboration avec des unites d'Universites, du CNRS, d'Instituts techniques et des firmes privees), appartenant a des stations de recherches implantees en differentes localisations geographiques (SUD-QUEST : BORDEAUX; SUD-EST: ANTIBES; EST : COLMAR; BASSIN PARISIEN : VERSAILLES) ont choisi cet insecte comme modele biologique et etudient les aspects suivants Selection - Selection de varietes resistantes du mais aux chenilles de la pyrale (Departement de Zoologie : BORDEAUX : P. ANGLADE, responsable du groupe I.W.G.O. (International Working Group on 0-0tlu.ruit nub�); Departement d'Am.i�lioration des plantes : MONTPELLIER : A. PANOUILLE ; F. KAAN). (1) (2) - 146 - Dynamique de population - Dynamique de population : evolutions qualitative et quantitative (larves, chrysalides, adultes, oeufs) et facteurs abiotiques; caracte risation thermique,en sommes de degres-jour,des evenements biologiques de la pyrale; recherche d'elements previsionnels et/ou indicateurs de l 'apparition des stades. (Departement de Zoologie : COLMAR : M. STENGEL; VERSAILLES : N. HAWLITZKY).(3)(4) - Modelisation de la dynamique de population : elaboration de saus modeles : saus modeles de developpement larvaire, de mortalite, de comportement larvaire, de degats et de rendement (Departement de Zoologie : VERSAILLES : B. GOT; J.M. LABATTE) en fonction des dates d'infestation, des stades phenologiques et des varietes, des facteurs cl imatiques. Sous modeles deja testes et valides au en cours de construction. D'autres saus modeles du cycle de la pyrale, complementaires des precedents,seront mis a l'etude ulterieurement. (5)(6)(7) - Physiologie du developpement et en particulier du developpement de diapause et de la levee de diapause dont les donnees seront prises en campte dans le saus modele de developpement. (Departement de Zoologie : VERSAILLES ; L. PEYPELUT, Universite de BORDEAUX; L. LAVENSEAU, effet d'analogue d'hormone juvenile sur ce developpement (VERSAILLES : G. GADENNE). (8)(9)(10) Dynamique et comportement : Relations "Plante-Insecte" - Dynamique de la ponte en fonction de la plante hote : choix du site de ponte par contact et intensite de pont,e en fonction de la nature de la plante hote (genre, variete, hybride) du stade phenolo gique, du niveau foliaire et du phylloplan (composition chimique et structure de la surface des feuilles. Composition liee au caractere intrinseque de la feuille et aux populations de bact2ries phyto pathogenes se developpant en epiphytes.(11)(12) - Recherche des facteurs responsables du choix. (Departement de Zoologie : VERSAILLES : S. DERRIDJ; P. BARRY; BORDEAUX : P. ANGLADE; Departement �e Physiologie vegetale : VERSAILLES : V. FIALA; J.P. BOUTIN; F. FERRON; Departement de Pathologie vegetale : VERSAILLES D. MARTIN; ANGERS : C. MANCEAU) .(13) - Comportement d'approche, de choix par contact de la plante hote et d'oviposition en fonction de la plante hote (espece veg�tale, variete, hybride, stade phenologique (Departement de Zoologie: VERSAILLES ENSH VERSAILLES : P. ROBERT). - Mise en evidence, role et nature de composants volatils des plantes hotes dans le comportement de reconnaissance ä distance. Cartographi e des structures sensorie 11 es et reponses el .ectrophys io- 1 ogi ques a ces composants (Departement de Zoologie : BURES SUR YVETTE: D. THIERRY et F. MARION POLL).(14) (15) - 147 - Dynamique de population et ennemis naturels : Relations "Insecte Insecte". - Dynamique de population d'insectes entomophages liberes en lachers inondatifs et saisonniers (Trichogrammes : T,u.chogJta.mma b1!.a.,6��cae Bezd., Hym. Trichogrammatidae) et coincidence spatio tempo relle avec la pyrale. Elaboration d'une methode .assurant d'une part le synchronisme des premieres pontes et 1 'emergence des oophages, d'autre part la couverture reguliere et complete de la periode de ponte du ravageur. L'ensemble de ces etudes a conduit a l 'elaboration d'une methode de lutte biologique mise en pratique, a 1 'echelle commerciale, depuis 1984 et a son affinement,actuellement,pour une efficacite maximale. (Departement de Zoologie : ANTIBES : J. VOEGELE; COLMAR : M. STENGEL; VERSAILLES : N. HAWLITZKY; U.N.C.A.A. : Union Nationale des Cooperatives Agricoles d'Approvisionnement : B. RAYNAUD). (16) - Caracteristiques biologiques des oophages en conditions controlees (J. VOEGELE), en conditions controlees, semi controlees et naturelles (N. HAWLITZKY et P. BARRY) sous 1 'effet des facteurs thermiques, hydriques et precipitations dont 1 'apport des donnees a contribue t 1 'elaboration de la methode de lutte (J. VOEGELE; N. HAWLITZKY) ä la mise au point d'un elevage de masse (J. VOEGELE; J. OAUMAL) et contribuera ä l'affinement de la methode de lutte (J. VOEGELE; N. HAWLITZKY; Universite PARIS-SUD, XI, G. LAUGE. (17) - Genetique du comportement de reconnaissance et d'oviposition de 1 'oophage (Departement de Zoologie : ANTIBES : E. WAJNBERG; Laboratoire de genetique : Universite de LYON : M. BOULETREAU).(18)(19) - Mise en evidence, role et nature chimique ae kairomones emanant de 1 'hote sur le comportement de recherche et de reconnais sance de 1 'oophage (Departement de Zoologie : VERSAILLES et U.N.C.A.A. N.HAWLITZKY; C. FRENOY; Departement de Phytopharmacie : VERSAILLES : M. RENOU; P. NANIAN). (20) - Mise au point de milieux artificiels et etude de 1 'oviposition et du developpement des Trichogrammes sur ces milieux. Action de kairomones sur 1 'oviposition dans des oeufs artificiels (Departement de Zoologie : LYON : S. GRENIER et G. BONNOT; VERSAILLES : N. HAWLITZKY et C. FRENOY; Departement de Phytopharmacie : M. RENOU). - D'autres travaux prenant place dans ces relations "insecte insecte" portent sur le cortege parasitaire des Tachinidae de la pyrale du mais (!)epartement de Zoologie : P. /\NGLAD�; P.GALICHET (AVIGNON); S. GRENIER; N. HAWLITKZY; AGPM : B. NAIBO et sur la physiologie du developpement de l 'un d'entre eux dans son hote naturel 0. YUlb.ila..UJ.i. (S. GRENIER). (21 )(22) Relations "Insecte - Champignon pathogene" Des etudes sont egalement conduites sur la pathogenecite de Beauve,u.a b���na. sur la pyrale du mais, sur la genetique des differentes souches, et son utilisation dans une lutte micro biologique contre les premiers stades larvaires. (Departement de Zoologie : VERSAILLES - LA MINIERE : G. RIBA). (23)(24) - 148 - Cet ensemble coherent de travaux de recherches doit permettre d'acquerir des connaissances de base sur le ravageur et ses ennemis naturels, d'expliquer les mecanismes regulant sa dynamique de popu lation et son comportement et d'estimer 1 'importance des facteurs abiotiques et biotiques qui les regissent. Ces connaissances entrent dans un objectif finalise : pratiquer une lutte integree en culture de mais, elaboree ä partir de recherches approfondies et s'appuyant sur une modelisation de la dynamique de population du ravageur, sur l'analyse de certains de ses comportements et sur 1 'uti1isation de methodes de lutte biologique tres elaborees. REFERENCES 1. ANGLADE, P., DERRIDJ, S., KAAN, F., PANOUILLE, A., (1986). Progress in the studies'of resistance to ECB (0.nu.b�I on maize in France. FouJtth mee.-ti.ng 06 the IOBC/WPRS Eaca.Jtpia. wo�lu.ng g�oap �eecU..ng 60� �v.;.u.,tance to in6ec-t6 and m.i;tv.;. Handv.;ted, Venma.Jtk. 23-25 septembre 1986. 2. ANGLADE, P., (1988). Conrnents Upon the Resistance and the Tolerance to the European Corn Borer of the Lines Tested in the IWGO Projects 1985-86 and 1987-88. P�oc. XVth S1J111p. Tnt. Wo�lu.ng g�oap an Oh:tlu.nia., Va.1tna, 167-170. 3. STENGEL, M., (1982). Essai de mise au point de la prevision des degats pour la lutte contre la pyrale du mais (Oh:tlu.nia. nab.ilaLl6l ° en Alsace (Est de la France). Entomophaga, 27, (n HS) 105-114. 4. HAWLITZKY, N., (1986). Etude de la biologie de la pyrale du mais, Oh:tlu.nia. nab.lla.R,.u., Hbn. (Lep. PylLa.Ltdael en region parisienne durant quatre annees et recherche d'elements previsionnels du debut de ponte. Acta oecotogica, Oecot. appl. 7, 47-68. 5. GOT, B., et RODOLPHE, F., (1989) Temperature-dependent model for European corn borer (Lepidoptera : Pyralidae) development. Env�on. Entomol., 18, 85-93. 6. GOT, B., LAVENSEAU, L., PEYPELUT, L., GADENNE, C., (1989). Modeli sation du cycle de la pyrale du mais (Oh:tlu.nia. nab�. Lepidop tera : Pyralidae). Illustration de deux niveaux de problemes : la duree de developpement larvaire et la diapause. Ann. Soc. ent. F� .• 24, 396. 7. LABATTE, J.M., Modelisation de la distribution verticale des larves de pyrale, Oh:tlu.nia. nabil� Hbn., sur la plant de mais. Soamih en janvi� 1990 a Jo�nat 06 apptied Entomology. 8. GADENNE, C., PEYPELUT, L., LAVENSEAU, L., et GOT, B., (1987). Utili sation de criteres metaboliques et morphogenetiques pour 1 'analyse de la diapause de populations naturelles d'Oh:tlu.nia. nabil� Hbn. Ag�onom-le, 10, 769-777. 9. PEYPELUT, L., BEVDON, P. et LAVENSEAU, L., (1990). Ecdysteroids metabolism during diapause breakdown in the European corn barer. Mchlve of IMect &i.oc.hem.u.,�y and Phyhiology. Sous Pr,esse. · · 10. GADENNE, C., GRENIER, S., PLANTEVIN, G. and MAUCHAMP, B., (1990). Effects of a juvenile hormone mimetic, fenoxycarb, on post embryonic development of the European corn barer. 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Detection des signaux allelochi miques volatils et comportement des .insectes phytophages. In : In6ectu, In6e.cticidu, Sante, ed. ACTA, 109-123. 15. MARION-POLL, F., (1986). La chimioreception chez la pyrale du mais I0-0� nub,Ua1.u,,Hbn.) : approche anatomique et el ectroantenno graphique. 158 p. (These Doct. Ingenieur "Sciences agronomiques", Institut National Agronomique Paris-Grignon). 16. HAWLITZKY, N., VOEGELE, J., STENGEL, M., REYNAUD, B., CROUZET, B., (1987). Utilisation de parasitoides oophages, les Trichogrammes dans la lutte contre la Pyrale du mais. 0-0tturu.a. nub.Uali.6 Hbn. (Lepidoptera, Pyralidae) : methodologie adoptee lors du passage de 1 'etat experimental a l 'utilisation en vraie grandeur. Con . 1, 0 Int. -0M .e.u Mva.gWM en a.gtucu.U.Me. Pa.tti-0, 2, 3 dec.7987. Ann. ANPP, 6, II, 191-198. 17. RUSSO, J. et VOEGELE, J., (1982a). Influence de la temperature sur quatre especes de Trichogrammes (Hym. 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